circular transaction log

Hi,
I have two important questions :
Question 1:
I need to know what the is the importance of transaction log file in MSSQL.
If we shrink our transaction log regularly, then would there be any negative
effect or loss of any useful feature in MSSQL.
Question 2:
In our scenario, the transaction log grows very fast because of the heavy DB
operations, so we need to shrink the transaction file regularly. I need a
way to create a circular log file in MSSQL so that it will automatically
overwrite the transaction log file when ever it reaches the maximum limit. I
know in oracle and DB2 this feature is there, but I could not find any
satisfactory Microsoft resource which tells can inform me how to create a
circular log file. Please help me out.
Best Regrads,
Abdul-Rahman"Abdul-Rahman" <rahman.mahmood@.pk.softecheww.com> wrote in message
news:%23AgZWGg3EHA.2600@.TK2MSFTNGP09.phx.gbl...
> Hi,
> I have two important questions :
> Question 1:
>
> I need to know what the is the importance of transaction log file in
> MSSQL.
> If we shrink our transaction log regularly, then would there be any
> negative
> effect or loss of any useful feature in MSSQL.
>
The transaction log is used for recovery. Without a transaction log you
will only be able to restore your database with a full backup. For instance
if you take full backups every night,
Here's a description of Sql Server recovery models.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/adminsql/ad_bkprst_60s9.asp
Under the Simple Recovery model your log file will be truncated at every
database checkpoint, and is only used to roll back failed transactions.
> Question 2:
>
> In our scenario, the transaction log grows very fast because of the heavy
> DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum limit.
> I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells can inform me how to create a
> circular log file. Please help me out.
>
The equivilent of Oracle's NOARCHIVELOG mode is Simple Recovery model. In
the full recovery model, with heavy use you will need to run a BACKUP LOG to
move the log somewhere safe and truncate it.
David|||"Abdul-Rahman" <rahman.mahmood@.pk.softecheww.com> wrote in message
news:%23AgZWGg3EHA.2600@.TK2MSFTNGP09.phx.gbl...
> Hi,
> I have two important questions :
> Question 1:
>
> I need to know what the is the importance of transaction log file in
MSSQL.
> If we shrink our transaction log regularly, then would there be any
negative
> effect or loss of any useful feature in MSSQL.
Shrinking the transaction log is generally a bad idea.
For one thing you risk getting disk level fragmentation. You're better off
creating a full size transaction log on a newly formatted disk and not
shrinking it.
In addition, if you keep shrinking it, you'll have to keep expanding it.
This takes time and can slow down your database.
Also, how are you clearing it out?
For production databases, you probably should be be doing backups as often
as necessary.
>
> Question 2:
>
> In our scenario, the transaction log grows very fast because of the heavy
DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum limit.
I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells can inform me how to create a
> circular log file. Please help me out.
>
Use Bulk Logged or Simple Recovery Mode. Books Online can go into more
detail.
However, keep in mind your decisions affect your recovery options.
>
>
> Best Regrads,
> Abdul-Rahman
>

circular transaction log

Hi,
I have two important questions :
Question 1:
I need to know what the is the importance of transaction log file in MSSQL.
If we shrink our transaction log regularly, then would there be any negative
effect or loss of any useful feature in MSSQL.
Question 2:
In our scenario, the transaction log grows very fast because of the heavy DB
operations, so we need to shrink the transaction file regularly. I need a
way to create a circular log file in MSSQL so that it will automatically
overwrite the transaction log file when ever it reaches the maximum limit. I
know in oracle and DB2 this feature is there, but I could not find any
satisfactory Microsoft resource which tells can inform me how to create a
circular log file. Please help me out.
Best Regrads,
Abdul-Rahman
"Abdul-Rahman" <rahman.mahmood@.pk.softecheww.com> wrote in message
news:%23AgZWGg3EHA.2600@.TK2MSFTNGP09.phx.gbl...
> Hi,
> I have two important questions :
> Question 1:
>
> I need to know what the is the importance of transaction log file in
> MSSQL.
> If we shrink our transaction log regularly, then would there be any
> negative
> effect or loss of any useful feature in MSSQL.
>
The transaction log is used for recovery. Without a transaction log you
will only be able to restore your database with a full backup. For instance
if you take full backups every night,
Here's a description of Sql Server recovery models.
http://msdn.microsoft.com/library/de...kprst_60s9.asp
Under the Simple Recovery model your log file will be truncated at every
database checkpoint, and is only used to roll back failed transactions.

> Question 2:
>
> In our scenario, the transaction log grows very fast because of the heavy
> DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum limit.
> I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells can inform me how to create a
> circular log file. Please help me out.
>
The equivilent of Oracle's NOARCHIVELOG mode is Simple Recovery model. In
the full recovery model, with heavy use you will need to run a BACKUP LOG to
move the log somewhere safe and truncate it.
David
|||"Abdul-Rahman" <rahman.mahmood@.pk.softecheww.com> wrote in message
news:%23AgZWGg3EHA.2600@.TK2MSFTNGP09.phx.gbl...
> Hi,
> I have two important questions :
> Question 1:
>
> I need to know what the is the importance of transaction log file in
MSSQL.
> If we shrink our transaction log regularly, then would there be any
negative
> effect or loss of any useful feature in MSSQL.
Shrinking the transaction log is generally a bad idea.
For one thing you risk getting disk level fragmentation. You're better off
creating a full size transaction log on a newly formatted disk and not
shrinking it.
In addition, if you keep shrinking it, you'll have to keep expanding it.
This takes time and can slow down your database.
Also, how are you clearing it out?
For production databases, you probably should be be doing backups as often
as necessary.

>
> Question 2:
>
> In our scenario, the transaction log grows very fast because of the heavy
DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum limit.
I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells can inform me how to create a
> circular log file. Please help me out.
>
Use Bulk Logged or Simple Recovery Mode. Books Online can go into more
detail.
However, keep in mind your decisions affect your recovery options.

>
>
> Best Regrads,
> Abdul-Rahman
>

Circular Reference?

I get this error when I ran the below statement what did I do wrong?

"The definition of MonthRange set contains a circular reference"

WITH SET [MonthRange] AS

{

[Dim Originationasofmm].[Dim Originationasofmm].&[200101].PrevMember

:

[Dim Originationasofmm].[Dim Originationasofmm].&[200101].NextMember

}

SELECT {[Measures].[Closing Balance]} on 0,

{[Dim Asofmm].FirstChild : [Dim Asofmm].[200612]} on 1

FROM [ Bond Analytics OLAP]

WHERE ([MonthRange], [Industry].&[Subprime])

[Dim Originationasofmm] is a regular dimension with members like 200101, 200102, 200103 so on.

What I wanted to do (Note that I do not have a Time Dimension in the cube, just a dimension that simulates this, so would this work just as well? )

Can I have a generic set that would take as input current member and give 3 or 6 or 12 rolling months?

(this is assuming that I cannot switch to using time dimension anytime soon and just have to use a regular dimension for now?)

For example,

given 200101 and say 3 for 3 months rolling period, I would get 200012, 200101, 200102

and

given 200101 and say 7 for 6 months rolling period, I would get 200010, 200011, 200012, 200101, 200102, 200103, 200104

Try this version:

WITH

SET [MonthRange] AS

LastPeriods(3,

[Dim Originationasofmm].[Dim Originationasofmm].&[200101].NextMember

)

MEMBER [Dim Originationasofmm].[Dim Originationasofmm].[MonthRange] as

Aggregate([MonthRange])

SELECT {[Measures].[Closing Balance]} on 0,

{[Dim Asofmm].FirstChild : [Dim Asofmm].[200612]} on 1

FROM [ Bond Analytics OLAP]

WHERE ([Dim Originationasofmm].[Dim Originationasofmm].[MonthRange],

[Industry].&[Subprime])

|||

Hi Deepark,

This query works! but as soon as I add any other measure below (1 or more) to the query, only column that has data would be [Closing Balance] and all other measures are NULL.

Is it because of some SCOPING issue in the calculation?

--Query only returns data for [Closing Balance], all other measures are NULL when they should have data.

WITH SET [MonthRange] AS
LastPeriods(3,[Dim Originationasofmm].[Dim Originationasofmm].&[200101].NextMember)

MEMBER [Dim Originationasofmm].[Dim Originationasofmm].[MonthRange] AS Aggregate([MonthRange])

SELECT {
[Measures].[Closing Balance],
[Measures].[D BankRuptcy],
[Measures].[D Foreclosure],
[Measures].[Def OTS]
} on 0,
{[Dim Asofmm].FirstChild:[Dim Asofmm].[200612]} on 1
FROM [Bond Analytics OLAP]
WHERE ([Dim Originationasofmm].[Dim Originationasofmm].[MonthRange],[Industry].&[Subprime])
GO

Calculations:

/* Rewrite of this to use SCOPE is below
CREATE MEMBER CURRENTCUBE.[MEASURES].[D BankRuptcy]
AS case when isempty([Measures].[Closing Balance]) Then Null
When [Dim MBA].currentmember IS [Dim MBA].[Bankruptcy] Then
([Dim MBA].[Bankruptcy],[Measures].[% by Delinquincy Currentbalance])
When [Dim MBA].currentmember IS [Dim MBA].[Current] Then Null
When [Dim MBA].currentmember is [Dim MBA].[All] then
([Dim MBA].[Bankruptcy],[Measures].[% By Delinquincy Currentbalance])
When [Dim MBA].currentmember is [Dim MBA].[MBA 30] then null
When [Dim MBA].currentmember is [Dim MBA].[MBA 60] then null
When [Dim MBA].currentmember is [Dim MBA].[MBA 90] then null
When [Dim MBA].currentmember is [Dim MBA].[Foreclosure] then null
When [Dim MBA].currentmember is [Dim MBA].[REO] then null
end,
FORMAT_STRING = "Percent",
VISIBLE = 1;
*/

CREATE MEMBER CURRENTCUBE.[MEASURES].[D BankRuptcy]
AS NULL,
VISIBLE = 1;

SCOPE([Measures].[D BankRuptcy]);
SCOPE(ROOT([Dim MBA]));
THIS = ([Dim MBA].[Bankruptcy],[Measures].[% by Delinquincy Currentbalance]);
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;

SCOPE ([Dim MBA].[Bankruptcy]);
THIS = ([Dim MBA].[Bankruptcy],[Measures].[% by Delinquincy Currentbalance]);
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;
END SCOPE;
-

/* Rewrite of this to use SCOPE is below
CREATE MEMBER CURRENTCUBE.[MEASURES].[D Foreclosure]
AS case when isempty([Measures].[Closing Balance]) Then Null
When [Dim MBA].currentmember IS [Dim MBA].[Foreclosure] Then
([Dim MBA].[Foreclosure],[Measures].[% by Delinquincy Currentbalance])
When [Dim MBA].currentmember IS [Dim MBA].[Current] Then Null
When [Dim MBA].currentmember is [Dim MBA].[All] then
([Dim MBA].[Foreclosure],[Measures].[% By Delinquincy Currentbalance])
When [Dim MBA].currentmember is [Dim MBA].[MBA 30] then null
When [Dim MBA].currentmember is [Dim MBA].[MBA 60] then null
When [Dim MBA].currentmember is [Dim MBA].[MBA 90] then null
When [Dim MBA].currentmember is [Dim MBA].[Bankruptcy] then null
When [Dim MBA].currentmember is [Dim MBA].[REO] then null
end,
FORMAT_STRING = "Percent",
VISIBLE = 1; */

CREATE MEMBER CURRENTCUBE.[MEASURES].[D Foreclosure]
AS NULL,
VISIBLE = 1;

SCOPE([Measures].[D Foreclosure]);
SCOPE(ROOT([Dim MBA]));
THIS = ([Dim MBA].[Foreclosure],[Measures].[% by Delinquincy Currentbalance]);
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;

SCOPE ([Dim MBA].[Foreclosure]);
THIS = ([Dim MBA].[Foreclosure],[Measures].[% by Delinquincy Currentbalance]);
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;
END SCOPE;
-

/* Rewrite of this to use SCOPE is below
CREATE MEMBER CURRENTCUBE.[MEASURES].[Def OTS]
AS case when isempty([Measures].[Closing Balance]) Then Null
When [Dim OTS].currentmember IS [Dim OTS].[OTS 30] Then Null
When [Dim OTS].currentmember IS [Dim OTS].[OTS 60] Then Null
When [Dim OTS].currentmember IS [Dim OTS].[OTS 90] Then Null
When [Dim OTS].currentmember IS [Dim OTS].[Bankruptcy] Then Null
When [Dim OTS].currentmember IS [Dim OTS].[Foreclosure] Then Null
When [Dim OTS].currentmember IS [Dim OTS].[Current] Then Null
When [Dim OTS].currentmember is [Dim OTS].[All] then
([Dim OTS].[REO],[Measures].[Closing Balance])
/([Dim OTS].[ALL],[Measures].[Closing Balance])
When [Dim OTS].currentmember is [Dim OTS].[REO]
then ([Measures].[Closing Balance]) /([Dim OTS].[REO],[Measures].[Closing Balance])
end,
VISIBLE = 1;
*/

CREATE MEMBER CURRENTCUBE.[MEASURES].[Def OTS]
AS NULL,
VISIBLE = 1;

SCOPE([Measures].[Def OTS]);
SCOPE(ROOT([Dim OTS]));
THIS = ([Dim OTS].[REO],[Measures].[Closing Balance])
/([Measures].[Closing Balance]);
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;

SCOPE ([Dim OTS].[REO]);
THIS = 1;
FORMAT_STRING(This) = "percent";
NON_EMPTY_BEHAVIOR(This) = [Measures].[Closing Balance];
END SCOPE;
END SCOPE;

|||

Well, I was able to reproduce this behavior in Adventure Works by creating a calculated measure with default value of NULL (as above); then just assigning it a constant value. But setting the new SP2 SCOPE_ISOLATION property seems to solve it - like:

MEMBER [Dim Originationasofmm].[Dim Originationasofmm].[MonthRange] AS Aggregate([MonthRange]),

SCOPE_ISOLATION = CUBE

|||

Hi Deepark,

Ok, so I don't know what SCOPE_ISOLATION does, but it works!!!

Perhaps, it is a new feature in SQL Server 2005 SP2.

Maybe it has something to do with calculation order.

Thank you very much.

You have helped me more than once (on many other discussion groups as well) and I am very grateful for that.

I think it's time you get a new title --> SUPER MVP

|||

Hi Deepark,

Ok, so I don't know what SCOPE_ISOLATION does, but it works!!!

Perhaps, it is a new feature in SQL Server 2005 SP2.

Maybe it has something to do with calculation order.

Thank you very much.

You have helped me more than once (on many other discussion groups as well) and I am very grateful for that.

I think it's time you get a new title --> SUPER MVP

by the way, the code that works look like this:

--so if I want another period, I just replace # 3 and [200101] with appropriate member chosen by the user.

--I wonder if I finally do have a Time dimension, would using CurrentMember work so I don't have to hard-code [200101]?

WITH SET [MonthRange] AS

LastPeriods(3,[Dim Originationasofmm].[Dim Originationasofmm].&[200101].NextMember)

MEMBER [Dim Originationasofmm].[Dim Originationasofmm].[MonthRange] AS Aggregate([MonthRange]),

SCOPE_ISOLATION = CUBE

SELECT {

[Measures].[Closing Balance],

[Measures].[D BankRuptcy],

[Measures].[D Foreclosure],

[Measures].[Def OTS],

[Measures].[D30 OTS],

[Measures].[D60 OTS],

[Measures].[D90 OTS]

} on 0,

{[Dim Asofmm].FirstChild:[Dim Asofmm].[200612]} on 1

FROM [Bond Analytics OLAP]

WHERE ([Dim Originationasofmm].[Dim Originationasofmm].[MonthRange],[Industry].&[Subprime])

GO

--this one also works, so if I want another rolling period, I just replace the lag #

WITH SET [MonthRange] AS

{[Dim Originationasofmm].&[200612].lag(1):[Dim Originationasofmm].&[200612].lag(-1)}

MEMBER [Dim Originationasofmm].[Dim Originationasofmm].[MonthRange] AS Aggregate([MonthRange]),

SCOPE_ISOLATION = CUBE

select

{

[Measures].[Closing Balance],

[Measures].[D BankRuptcy],

[Measures].[D Foreclosure],

[Measures].[Def OTS],

[Measures].[D30 OTS],

[Measures].[D60 OTS],

[Measures].[D90 OTS]

} on 0,

([Dim Asofmm].FIRSTchild:[Dim Asofmm].[200612]) on 1

from [Bond Analytics OLAP]

WHERE ([Dim Originationasofmm].[Dim Originationasofmm].[MonthRange],[Industry].&[Subprime])

Circular reference

I would like to know if there is a problem when I create a Work with several
steps and the last step call first step again?Can you give a specific example of what you mean by work? Some recursive
operations (like a trigger) can only be nested 16 levels deep.
Brian
"Mariano Arias" <Mariano Arias@.discussions.microsoft.com> wrote in message
news:96505317-0C08-4A2F-9DCA-CA1FE75A3F30@.microsoft.com...
> I would like to know if there is a problem when I create a Work with
several steps and the last step call first step again?

Circular reference

I would like to know if there is a problem when I create a Work with several steps and the last step call first step again?
Can you give a specific example of what you mean by work? Some recursive
operations (like a trigger) can only be nested 16 levels deep.
Brian
"Mariano Arias" <Mariano Arias@.discussions.microsoft.com> wrote in message
news:96505317-0C08-4A2F-9DCA-CA1FE75A3F30@.microsoft.com...
> I would like to know if there is a problem when I create a Work with
several steps and the last step call first step again?

circular log

Hi,
I have 2 questions:
Question 1:
I need to know what the importance of the transaction log file is. If we
shrink our transaction log regularly, then would there be any negative
effect or loss of any useful feature in MSSQL.
Question 2:
In our scenario, the transaction log grows very fast because of the heavy DB
operations, so we need to shrink the transaction file regularly. I need a
way to create a circular log file in MSSQL so that it will automatically
overwrite the transaction log file when ever it reaches the maximum limit. I
know in oracle and DB2 this feature is there, but I could not find any
satisfactory Microsoft resource which tells us how to create a circular log
file. Please help me out
Best Regards,
Abdul-Rahman.
> Hi,
> I have 2 questions:
>
> Question 1:
> I need to know what the importance of the transaction log file is.
The transaction log allows point-in-time data recovery.

> If we shrink our transaction log regularly, then would there be any
negative
> effect or loss of any useful feature in MSSQL.
It is safe to truncate the transaction log regularly by backing up the
transaction log regularly.

> Question 2:
> In our scenario, the transaction log grows very fast because of the heavy
DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum
limit. I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells us how to create a circular
log
> file. Please help me out
There is no circular log in SQL Server. Do you need point-in-time recovery?
If not, you can use a SIMPLE RECOVERY model for your database. Or you can
keep your FULL RECOVERY MODEL and backup your transaction logs more
frequently. Backing up your transaction log will truncate it.
Hope this helps,
Eric Crdenas
Support professional
This posting is provided "AS IS" with no warranties, and confers no rights.

circular log

Hi,
I have 2 questions:
Question 1:
I need to know what the importance of the transaction log file is. If we
shrink our transaction log regularly, then would there be any negative
effect or loss of any useful feature in MSSQL.
Question 2:
In our scenario, the transaction log grows very fast because of the heavy DB
operations, so we need to shrink the transaction file regularly. I need a
way to create a circular log file in MSSQL so that it will automatically
overwrite the transaction log file when ever it reaches the maximum limit. I
know in oracle and DB2 this feature is there, but I could not find any
satisfactory Microsoft resource which tells us how to create a circular log
file. Please help me out
Best Regards,
Abdul-Rahman.> Hi,
> I have 2 questions:
>
> Question 1:
> I need to know what the importance of the transaction log file is.
--
The transaction log allows point-in-time data recovery.
> If we shrink our transaction log regularly, then would there be any
negative
> effect or loss of any useful feature in MSSQL.
--
It is safe to truncate the transaction log regularly by backing up the
transaction log regularly.
> Question 2:
> In our scenario, the transaction log grows very fast because of the heavy
DB
> operations, so we need to shrink the transaction file regularly. I need a
> way to create a circular log file in MSSQL so that it will automatically
> overwrite the transaction log file when ever it reaches the maximum
limit. I
> know in oracle and DB2 this feature is there, but I could not find any
> satisfactory Microsoft resource which tells us how to create a circular
log
> file. Please help me out
--
There is no circular log in SQL Server. Do you need point-in-time recovery?
If not, you can use a SIMPLE RECOVERY model for your database. Or you can
keep your FULL RECOVERY MODEL and backup your transaction logs more
frequently. Backing up your transaction log will truncate it.
Hope this helps,
--
Eric Cárdenas
Support professional
This posting is provided "AS IS" with no warranties, and confers no rights.sqlsql

Circular FK Constraints

Hi.
My system includes Clients and Contacts in a many-to-many relationship
handled in the usual way using a link table with a primary key of Client key
plus Contact key and foreign key constraints against Client and Contact
tables. Each Client may have a Main Contact, which is handled at present wit
h
a 'Main Contact' column in the Client table, which for referential integrity
has a foreign key constraint against the link table. These circular FK
constraints are a nuisance when it comes to deleting a client. I suppose I
could use a trigger to enforce referential integrity, but I don't want to -
the Client table already has a rather complicated trigger.
Can anyone think of a better way?
Thanks.
--
Peter HyssettPeter Hyssett wrote:
> Hi.
> My system includes Clients and Contacts in a many-to-many relationship
> handled in the usual way using a link table with a primary key of Client k
ey
> plus Contact key and foreign key constraints against Client and Contact
> tables. Each Client may have a Main Contact, which is handled at present w
ith
> a 'Main Contact' column in the Client table, which for referential integri
ty
> has a foreign key constraint against the link table. These circular FK
> constraints are a nuisance when it comes to deleting a client. I suppose I
> could use a trigger to enforce referential integrity, but I don't want to
-
> the Client table already has a rather complicated trigger.
> Can anyone think of a better way?
> Thanks.
Well, in my mind, your main contact fk would be better off referencing
the contact table instead of the link table.
When deleting a contact, you would obviously need to either set the
client.main contact column to a valid id from the contact table first,
or set it to null whichever is appropriate.
Then you should be fine.
JB|||Thanks. I'm afraid the FK is against the link table because the main contact
must be a contact already linked to the client, which an FK against the
Contact table would not enforce. Nowadays I do set the Main Contact column t
o
NULL before deleting (the link table rows being deleted first), but I would
prefer not to.
--
Peter Hyssett
"John B" wrote:

> Peter Hyssett wrote:
> Well, in my mind, your main contact fk would be better off referencing
> the contact table instead of the link table.
> When deleting a contact, you would obviously need to either set the
> client.main contact column to a valid id from the contact table first,
> or set it to null whichever is appropriate.
> Then you should be fine.
> JB
>|||Hello, Peter
As I understand this, your DDL is (or should be) something like this:
CREATE TABLE Contacts (
ContactID int PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns...
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns...
MainContactID int NULL
)
CREATE TABLE ClientContacts (
ClientID int REFERENCES Clients ON DELETE CASCADE,
ContactID int REFERENCES Contacts ON DELETE CASCADE,
PRIMARY KEY (ClientID, ContactID)
)
ALTER TABLE Clients ADD CONSTRAINT TheFK
FOREIGN KEY (ClientID, MainContactID)
REFERENCES ClientContacts (ClientID, ContactID)
Assuming the following sample data:
SET NOCOUNT ON
INSERT INTO Clients (ClientID, ClientName)
VALUES (100, 'Big Company, Inc.')
INSERT INTO Contacts VALUES (1, 'John', 'Smith')
INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
INSERT INTO ClientContacts VALUES (100, 1)
INSERT INTO ClientContacts VALUES (100, 2)
UPDATE Clients SET MainContactID=1 WHERE ClientID=100
INSERT INTO Clients (ClientID, ClientName)
VALUES (200, 'Another Company, Ltd.')
INSERT INTO Contacts VALUES (3, 'John', 'Doe')
INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
INSERT INTO ClientContacts VALUES (200, 2)
INSERT INTO ClientContacts VALUES (200, 3)
INSERT INTO ClientContacts VALUES (200, 4)
UPDATE Clients SET MainContactID=3 WHERE ClientID=200
SET NOCOUNT OFF
Let's suppose you want to delete the client with the ClientID=100.
Using a simple "DELETE Clients WHERE ClientID=100" works (without any
error): the client is deleted and it's links with the contacts, too
(but the contacts themselves remain). If you want to also delete the
contacts (the ones that are not linked with any other client), you can
use the following trigger:
CREATE TRIGGER Clients_DeleteContacts ON Clients
INSTEAD OF DELETE
AS
IF @.@.ROWCOUNT>0 BEGIN
SET NOCOUNT ON
UPDATE Clients SET MainContactID=NULL
WHERE ClientID IN (SELECT ClientID FROM deleted)
DELETE Contacts WHERE ContactID IN (
SELECT x.ContactID FROM ClientContacts x
WHERE x.ClientID IN (SELECT ClientID FROM deleted)
AND NOT EXISTS (
SELECT * FROM ClientContacts y
WHERE x.ContactID=y.ContactID
AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
)
)
DELETE Clients
WHERE ClientID IN (SELECT ClientID FROM deleted)
END
Razvan|||On Thu, 16 Jun 2005 16:19:05 -0700, Peter Hyssett wrote:

>Hi.
>My system includes Clients and Contacts in a many-to-many relationship
>handled in the usual way using a link table with a primary key of Client ke
y
>plus Contact key and foreign key constraints against Client and Contact
>tables. Each Client may have a Main Contact, which is handled at present wi
th
>a 'Main Contact' column in the Client table, which for referential integrit
y
>has a foreign key constraint against the link table. These circular FK
>constraints are a nuisance when it comes to deleting a client. I suppose I
>could use a trigger to enforce referential integrity, but I don't want to -
>the Client table already has a rather complicated trigger.
>Can anyone think of a better way?
>Thanks.
Hi Peter,
I'd consider something like this (stealing lots from Razvan Socol's
post)
CREATE TABLE Contacts (
ContactID int NOT NULL PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns--
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int NOT NULL PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns--
)
CREATE TABLE ClientContacts (
ClientID int NOT NULL REFERENCES Clients ON DELETE CASCADE,
ContactID int NOT NULL REFERENCES Contacts ON DELETE CASCADE,
Priority smallint NOT NULL CHECK Priority > 0,
PRIMARY KEY (ClientID, ContactID),
UNIQUE (ClientID, Priority)
)
CREATE VIEW PrimaryContact
AS
SELECT cc.ClientID, cc.ContactID
FROM (SELECT ClientID, MIN(Priority) AS MinPrio
FROM ClientContacts
GROUP BY ClientID) AS d
INNER JOIN ClientContacts AS cc
ON cc.ClientID = d.ClientID
AND cc.Priority = d.MinPrio
go
Best, Hugo
--
(Remove _NO_ and _SPAM_ to get my e-mail address)|||Peter Hyssett wrote:
> Thanks. I'm afraid the FK is against the link table because the main conta
ct
> must be a contact already linked to the client,
Ah, that makes sense
> which an FK against the
> Contact table would not enforce. Nowadays I do set the Main Contact column
to
> NULL before deleting (the link table rows being deleted first), but I woul
d
> prefer not to.
Why would you prefer not to?
Cascade delete _might_ set it to null but Im not sure.
If you wished to keep the MainContactId, then it would be a referential
break as the actual contact would have been deleted.
You could do this by removing the FK constraint though.
JB|||Thanks, Razvan. The ON DELETE CASCADE construct is what I wanted - I just
hadn't come across it before.
Cheers,
Peter.
Peter Hyssett
"Razvan Socol" wrote:

> Hello, Peter
> As I understand this, your DDL is (or should be) something like this:
> CREATE TABLE Contacts (
> ContactID int PRIMARY KEY,
> FirstName varchar(30) NOT NULL,
> LastName varchar(20) NOT NULL,
> --other columns...
> UNIQUE (FirstName, LastName)
> )
> CREATE TABLE Clients (
> ClientID int PRIMARY KEY,
> ClientName varchar(50) NOT NULL UNIQUE,
> --other columns...
> MainContactID int NULL
> )
> CREATE TABLE ClientContacts (
> ClientID int REFERENCES Clients ON DELETE CASCADE,
> ContactID int REFERENCES Contacts ON DELETE CASCADE,
> PRIMARY KEY (ClientID, ContactID)
> )
> ALTER TABLE Clients ADD CONSTRAINT TheFK
> FOREIGN KEY (ClientID, MainContactID)
> REFERENCES ClientContacts (ClientID, ContactID)
>
> Assuming the following sample data:
> SET NOCOUNT ON
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (100, 'Big Company, Inc.')
> INSERT INTO Contacts VALUES (1, 'John', 'Smith')
> INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
> INSERT INTO ClientContacts VALUES (100, 1)
> INSERT INTO ClientContacts VALUES (100, 2)
> UPDATE Clients SET MainContactID=1 WHERE ClientID=100
>
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (200, 'Another Company, Ltd.')
> INSERT INTO Contacts VALUES (3, 'John', 'Doe')
> INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
> INSERT INTO ClientContacts VALUES (200, 2)
> INSERT INTO ClientContacts VALUES (200, 3)
> INSERT INTO ClientContacts VALUES (200, 4)
> UPDATE Clients SET MainContactID=3 WHERE ClientID=200
> SET NOCOUNT OFF
>
> Let's suppose you want to delete the client with the ClientID=100.
> Using a simple "DELETE Clients WHERE ClientID=100" works (without any
> error): the client is deleted and it's links with the contacts, too
> (but the contacts themselves remain). If you want to also delete the
> contacts (the ones that are not linked with any other client), you can
> use the following trigger:
> CREATE TRIGGER Clients_DeleteContacts ON Clients
> INSTEAD OF DELETE
> AS
> IF @.@.ROWCOUNT>0 BEGIN
> SET NOCOUNT ON
> UPDATE Clients SET MainContactID=NULL
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> DELETE Contacts WHERE ContactID IN (
> SELECT x.ContactID FROM ClientContacts x
> WHERE x.ClientID IN (SELECT ClientID FROM deleted)
> AND NOT EXISTS (
> SELECT * FROM ClientContacts y
> WHERE x.ContactID=y.ContactID
> AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
> )
> )
> DELETE Clients
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> END
> Razvan
>

Circular FK Constraints

Hi.
My system includes Clients and Contacts in a many-to-many relationship
handled in the usual way using a link table with a primary key of Client key
plus Contact key and foreign key constraints against Client and Contact
tables. Each Client may have a Main Contact, which is handled at present with
a 'Main Contact' column in the Client table, which for referential integrity
has a foreign key constraint against the link table. These circular FK
constraints are a nuisance when it comes to deleting a client. I suppose I
could use a trigger to enforce referential integrity, but I don't want to -
the Client table already has a rather complicated trigger.
Can anyone think of a better way?
Thanks.
--
Peter HyssettPeter Hyssett wrote:
> Hi.
> My system includes Clients and Contacts in a many-to-many relationship
> handled in the usual way using a link table with a primary key of Client key
> plus Contact key and foreign key constraints against Client and Contact
> tables. Each Client may have a Main Contact, which is handled at present with
> a 'Main Contact' column in the Client table, which for referential integrity
> has a foreign key constraint against the link table. These circular FK
> constraints are a nuisance when it comes to deleting a client. I suppose I
> could use a trigger to enforce referential integrity, but I don't want to -
> the Client table already has a rather complicated trigger.
> Can anyone think of a better way?
> Thanks.
Well, in my mind, your main contact fk would be better off referencing
the contact table instead of the link table.
When deleting a contact, you would obviously need to either set the
client.main contact column to a valid id from the contact table first,
or set it to null whichever is appropriate.
Then you should be fine.
JB|||Thanks. I'm afraid the FK is against the link table because the main contact
must be a contact already linked to the client, which an FK against the
Contact table would not enforce. Nowadays I do set the Main Contact column to
NULL before deleting (the link table rows being deleted first), but I would
prefer not to.
--
Peter Hyssett
"John B" wrote:
> Peter Hyssett wrote:
> > Hi.
> > My system includes Clients and Contacts in a many-to-many relationship
> > handled in the usual way using a link table with a primary key of Client key
> > plus Contact key and foreign key constraints against Client and Contact
> > tables. Each Client may have a Main Contact, which is handled at present with
> > a 'Main Contact' column in the Client table, which for referential integrity
> > has a foreign key constraint against the link table. These circular FK
> > constraints are a nuisance when it comes to deleting a client. I suppose I
> > could use a trigger to enforce referential integrity, but I don't want to -
> > the Client table already has a rather complicated trigger.
> >
> > Can anyone think of a better way?
> >
> > Thanks.
> Well, in my mind, your main contact fk would be better off referencing
> the contact table instead of the link table.
> When deleting a contact, you would obviously need to either set the
> client.main contact column to a valid id from the contact table first,
> or set it to null whichever is appropriate.
> Then you should be fine.
> JB
>|||Hello, Peter
As I understand this, your DDL is (or should be) something like this:
CREATE TABLE Contacts (
ContactID int PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns...
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns...
MainContactID int NULL
)
CREATE TABLE ClientContacts (
ClientID int REFERENCES Clients ON DELETE CASCADE,
ContactID int REFERENCES Contacts ON DELETE CASCADE,
PRIMARY KEY (ClientID, ContactID)
)
ALTER TABLE Clients ADD CONSTRAINT TheFK
FOREIGN KEY (ClientID, MainContactID)
REFERENCES ClientContacts (ClientID, ContactID)
Assuming the following sample data:
SET NOCOUNT ON
INSERT INTO Clients (ClientID, ClientName)
VALUES (100, 'Big Company, Inc.')
INSERT INTO Contacts VALUES (1, 'John', 'Smith')
INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
INSERT INTO ClientContacts VALUES (100, 1)
INSERT INTO ClientContacts VALUES (100, 2)
UPDATE Clients SET MainContactID=1 WHERE ClientID=100
INSERT INTO Clients (ClientID, ClientName)
VALUES (200, 'Another Company, Ltd.')
INSERT INTO Contacts VALUES (3, 'John', 'Doe')
INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
INSERT INTO ClientContacts VALUES (200, 2)
INSERT INTO ClientContacts VALUES (200, 3)
INSERT INTO ClientContacts VALUES (200, 4)
UPDATE Clients SET MainContactID=3 WHERE ClientID=200
SET NOCOUNT OFF
Let's suppose you want to delete the client with the ClientID=100.
Using a simple "DELETE Clients WHERE ClientID=100" works (without any
error): the client is deleted and it's links with the contacts, too
(but the contacts themselves remain). If you want to also delete the
contacts (the ones that are not linked with any other client), you can
use the following trigger:
CREATE TRIGGER Clients_DeleteContacts ON Clients
INSTEAD OF DELETE
AS
IF @.@.ROWCOUNT>0 BEGIN
SET NOCOUNT ON
UPDATE Clients SET MainContactID=NULL
WHERE ClientID IN (SELECT ClientID FROM deleted)
DELETE Contacts WHERE ContactID IN (
SELECT x.ContactID FROM ClientContacts x
WHERE x.ClientID IN (SELECT ClientID FROM deleted)
AND NOT EXISTS (
SELECT * FROM ClientContacts y
WHERE x.ContactID=y.ContactID
AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
)
)
DELETE Clients
WHERE ClientID IN (SELECT ClientID FROM deleted)
END
Razvan|||On Thu, 16 Jun 2005 16:19:05 -0700, Peter Hyssett wrote:
>Hi.
>My system includes Clients and Contacts in a many-to-many relationship
>handled in the usual way using a link table with a primary key of Client key
>plus Contact key and foreign key constraints against Client and Contact
>tables. Each Client may have a Main Contact, which is handled at present with
>a 'Main Contact' column in the Client table, which for referential integrity
>has a foreign key constraint against the link table. These circular FK
>constraints are a nuisance when it comes to deleting a client. I suppose I
>could use a trigger to enforce referential integrity, but I don't want to -
>the Client table already has a rather complicated trigger.
>Can anyone think of a better way?
>Thanks.
Hi Peter,
I'd consider something like this (stealing lots from Razvan Socol's
post)
CREATE TABLE Contacts (
ContactID int NOT NULL PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns--
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int NOT NULL PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns--
)
CREATE TABLE ClientContacts (
ClientID int NOT NULL REFERENCES Clients ON DELETE CASCADE,
ContactID int NOT NULL REFERENCES Contacts ON DELETE CASCADE,
Priority smallint NOT NULL CHECK Priority > 0,
PRIMARY KEY (ClientID, ContactID),
UNIQUE (ClientID, Priority)
)
CREATE VIEW PrimaryContact
AS
SELECT cc.ClientID, cc.ContactID
FROM (SELECT ClientID, MIN(Priority) AS MinPrio
FROM ClientContacts
GROUP BY ClientID) AS d
INNER JOIN ClientContacts AS cc
ON cc.ClientID = d.ClientID
AND cc.Priority = d.MinPrio
go
Best, Hugo
--
(Remove _NO_ and _SPAM_ to get my e-mail address)|||Peter Hyssett wrote:
> Thanks. I'm afraid the FK is against the link table because the main contact
> must be a contact already linked to the client,
Ah, that makes sense
> which an FK against the
> Contact table would not enforce. Nowadays I do set the Main Contact column to
> NULL before deleting (the link table rows being deleted first), but I would
> prefer not to.
Why would you prefer not to?
Cascade delete _might_ set it to null but Im not sure.
If you wished to keep the MainContactId, then it would be a referential
break as the actual contact would have been deleted.
You could do this by removing the FK constraint though.
JB|||Thanks, Razvan. The ON DELETE CASCADE construct is what I wanted - I just
hadn't come across it before.
Cheers,
Peter.
--
Peter Hyssett
"Razvan Socol" wrote:
> Hello, Peter
> As I understand this, your DDL is (or should be) something like this:
> CREATE TABLE Contacts (
> ContactID int PRIMARY KEY,
> FirstName varchar(30) NOT NULL,
> LastName varchar(20) NOT NULL,
> --other columns...
> UNIQUE (FirstName, LastName)
> )
> CREATE TABLE Clients (
> ClientID int PRIMARY KEY,
> ClientName varchar(50) NOT NULL UNIQUE,
> --other columns...
> MainContactID int NULL
> )
> CREATE TABLE ClientContacts (
> ClientID int REFERENCES Clients ON DELETE CASCADE,
> ContactID int REFERENCES Contacts ON DELETE CASCADE,
> PRIMARY KEY (ClientID, ContactID)
> )
> ALTER TABLE Clients ADD CONSTRAINT TheFK
> FOREIGN KEY (ClientID, MainContactID)
> REFERENCES ClientContacts (ClientID, ContactID)
>
> Assuming the following sample data:
> SET NOCOUNT ON
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (100, 'Big Company, Inc.')
> INSERT INTO Contacts VALUES (1, 'John', 'Smith')
> INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
> INSERT INTO ClientContacts VALUES (100, 1)
> INSERT INTO ClientContacts VALUES (100, 2)
> UPDATE Clients SET MainContactID=1 WHERE ClientID=100
>
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (200, 'Another Company, Ltd.')
> INSERT INTO Contacts VALUES (3, 'John', 'Doe')
> INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
> INSERT INTO ClientContacts VALUES (200, 2)
> INSERT INTO ClientContacts VALUES (200, 3)
> INSERT INTO ClientContacts VALUES (200, 4)
> UPDATE Clients SET MainContactID=3 WHERE ClientID=200
> SET NOCOUNT OFF
>
> Let's suppose you want to delete the client with the ClientID=100.
> Using a simple "DELETE Clients WHERE ClientID=100" works (without any
> error): the client is deleted and it's links with the contacts, too
> (but the contacts themselves remain). If you want to also delete the
> contacts (the ones that are not linked with any other client), you can
> use the following trigger:
> CREATE TRIGGER Clients_DeleteContacts ON Clients
> INSTEAD OF DELETE
> AS
> IF @.@.ROWCOUNT>0 BEGIN
> SET NOCOUNT ON
> UPDATE Clients SET MainContactID=NULL
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> DELETE Contacts WHERE ContactID IN (
> SELECT x.ContactID FROM ClientContacts x
> WHERE x.ClientID IN (SELECT ClientID FROM deleted)
> AND NOT EXISTS (
> SELECT * FROM ClientContacts y
> WHERE x.ContactID=y.ContactID
> AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
> )
> )
> DELETE Clients
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> END
> Razvan
>

Circular FK Constraints

Hi.
My system includes Clients and Contacts in a many-to-many relationship
handled in the usual way using a link table with a primary key of Client key
plus Contact key and foreign key constraints against Client and Contact
tables. Each Client may have a Main Contact, which is handled at present with
a 'Main Contact' column in the Client table, which for referential integrity
has a foreign key constraint against the link table. These circular FK
constraints are a nuisance when it comes to deleting a client. I suppose I
could use a trigger to enforce referential integrity, but I don't want to -
the Client table already has a rather complicated trigger.
Can anyone think of a better way?
Thanks.
Peter Hyssett
Peter Hyssett wrote:
> Hi.
> My system includes Clients and Contacts in a many-to-many relationship
> handled in the usual way using a link table with a primary key of Client key
> plus Contact key and foreign key constraints against Client and Contact
> tables. Each Client may have a Main Contact, which is handled at present with
> a 'Main Contact' column in the Client table, which for referential integrity
> has a foreign key constraint against the link table. These circular FK
> constraints are a nuisance when it comes to deleting a client. I suppose I
> could use a trigger to enforce referential integrity, but I don't want to -
> the Client table already has a rather complicated trigger.
> Can anyone think of a better way?
> Thanks.
Well, in my mind, your main contact fk would be better off referencing
the contact table instead of the link table.
When deleting a contact, you would obviously need to either set the
client.main contact column to a valid id from the contact table first,
or set it to null whichever is appropriate.
Then you should be fine.
JB
|||Thanks. I'm afraid the FK is against the link table because the main contact
must be a contact already linked to the client, which an FK against the
Contact table would not enforce. Nowadays I do set the Main Contact column to
NULL before deleting (the link table rows being deleted first), but I would
prefer not to.
Peter Hyssett
"John B" wrote:

> Peter Hyssett wrote:
> Well, in my mind, your main contact fk would be better off referencing
> the contact table instead of the link table.
> When deleting a contact, you would obviously need to either set the
> client.main contact column to a valid id from the contact table first,
> or set it to null whichever is appropriate.
> Then you should be fine.
> JB
>
|||Hello, Peter
As I understand this, your DDL is (or should be) something like this:
CREATE TABLE Contacts (
ContactID int PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns...
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns...
MainContactID int NULL
)
CREATE TABLE ClientContacts (
ClientID int REFERENCES Clients ON DELETE CASCADE,
ContactID int REFERENCES Contacts ON DELETE CASCADE,
PRIMARY KEY (ClientID, ContactID)
)
ALTER TABLE Clients ADD CONSTRAINT TheFK
FOREIGN KEY (ClientID, MainContactID)
REFERENCES ClientContacts (ClientID, ContactID)
Assuming the following sample data:
SET NOCOUNT ON
INSERT INTO Clients (ClientID, ClientName)
VALUES (100, 'Big Company, Inc.')
INSERT INTO Contacts VALUES (1, 'John', 'Smith')
INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
INSERT INTO ClientContacts VALUES (100, 1)
INSERT INTO ClientContacts VALUES (100, 2)
UPDATE Clients SET MainContactID=1 WHERE ClientID=100
INSERT INTO Clients (ClientID, ClientName)
VALUES (200, 'Another Company, Ltd.')
INSERT INTO Contacts VALUES (3, 'John', 'Doe')
INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
INSERT INTO ClientContacts VALUES (200, 2)
INSERT INTO ClientContacts VALUES (200, 3)
INSERT INTO ClientContacts VALUES (200, 4)
UPDATE Clients SET MainContactID=3 WHERE ClientID=200
SET NOCOUNT OFF
Let's suppose you want to delete the client with the ClientID=100.
Using a simple "DELETE Clients WHERE ClientID=100" works (without any
error): the client is deleted and it's links with the contacts, too
(but the contacts themselves remain). If you want to also delete the
contacts (the ones that are not linked with any other client), you can
use the following trigger:
CREATE TRIGGER Clients_DeleteContacts ON Clients
INSTEAD OF DELETE
AS
IF @.@.ROWCOUNT>0 BEGIN
SET NOCOUNT ON
UPDATE Clients SET MainContactID=NULL
WHERE ClientID IN (SELECT ClientID FROM deleted)
DELETE Contacts WHERE ContactID IN (
SELECT x.ContactID FROM ClientContacts x
WHERE x.ClientID IN (SELECT ClientID FROM deleted)
AND NOT EXISTS (
SELECT * FROM ClientContacts y
WHERE x.ContactID=y.ContactID
AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
)
)
DELETE Clients
WHERE ClientID IN (SELECT ClientID FROM deleted)
END
Razvan
|||On Thu, 16 Jun 2005 16:19:05 -0700, Peter Hyssett wrote:

>Hi.
>My system includes Clients and Contacts in a many-to-many relationship
>handled in the usual way using a link table with a primary key of Client key
>plus Contact key and foreign key constraints against Client and Contact
>tables. Each Client may have a Main Contact, which is handled at present with
>a 'Main Contact' column in the Client table, which for referential integrity
>has a foreign key constraint against the link table. These circular FK
>constraints are a nuisance when it comes to deleting a client. I suppose I
>could use a trigger to enforce referential integrity, but I don't want to -
>the Client table already has a rather complicated trigger.
>Can anyone think of a better way?
>Thanks.
Hi Peter,
I'd consider something like this (stealing lots from Razvan Socol's
post)
CREATE TABLE Contacts (
ContactID int NOT NULL PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(20) NOT NULL,
--other columns--
UNIQUE (FirstName, LastName)
)
CREATE TABLE Clients (
ClientID int NOT NULL PRIMARY KEY,
ClientName varchar(50) NOT NULL UNIQUE,
--other columns--
)
CREATE TABLE ClientContacts (
ClientID int NOT NULL REFERENCES Clients ON DELETE CASCADE,
ContactID int NOT NULL REFERENCES Contacts ON DELETE CASCADE,
Priority smallint NOT NULL CHECK Priority > 0,
PRIMARY KEY (ClientID, ContactID),
UNIQUE (ClientID, Priority)
)
CREATE VIEW PrimaryContact
AS
SELECT cc.ClientID, cc.ContactID
FROM (SELECT ClientID, MIN(Priority) AS MinPrio
FROM ClientContacts
GROUP BY ClientID) AS d
INNER JOIN ClientContacts AS cc
ON cc.ClientID = d.ClientID
AND cc.Priority = d.MinPrio
go
Best, Hugo
(Remove _NO_ and _SPAM_ to get my e-mail address)
|||Peter Hyssett wrote:
> Thanks. I'm afraid the FK is against the link table because the main contact
> must be a contact already linked to the client,
Ah, that makes sense
> which an FK against the
> Contact table would not enforce. Nowadays I do set the Main Contact column to
> NULL before deleting (the link table rows being deleted first), but I would
> prefer not to.
Why would you prefer not to?
Cascade delete _might_ set it to null but Im not sure.
If you wished to keep the MainContactId, then it would be a referential
break as the actual contact would have been deleted.
You could do this by removing the FK constraint though.
JB
|||Thanks, Razvan. The ON DELETE CASCADE construct is what I wanted - I just
hadn't come across it before.
Cheers,
Peter.
Peter Hyssett
"Razvan Socol" wrote:

> Hello, Peter
> As I understand this, your DDL is (or should be) something like this:
> CREATE TABLE Contacts (
> ContactID int PRIMARY KEY,
> FirstName varchar(30) NOT NULL,
> LastName varchar(20) NOT NULL,
> --other columns...
> UNIQUE (FirstName, LastName)
> )
> CREATE TABLE Clients (
> ClientID int PRIMARY KEY,
> ClientName varchar(50) NOT NULL UNIQUE,
> --other columns...
> MainContactID int NULL
> )
> CREATE TABLE ClientContacts (
> ClientID int REFERENCES Clients ON DELETE CASCADE,
> ContactID int REFERENCES Contacts ON DELETE CASCADE,
> PRIMARY KEY (ClientID, ContactID)
> )
> ALTER TABLE Clients ADD CONSTRAINT TheFK
> FOREIGN KEY (ClientID, MainContactID)
> REFERENCES ClientContacts (ClientID, ContactID)
>
> Assuming the following sample data:
> SET NOCOUNT ON
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (100, 'Big Company, Inc.')
> INSERT INTO Contacts VALUES (1, 'John', 'Smith')
> INSERT INTO Contacts VALUES (2, 'Mary', 'Smith')
> INSERT INTO ClientContacts VALUES (100, 1)
> INSERT INTO ClientContacts VALUES (100, 2)
> UPDATE Clients SET MainContactID=1 WHERE ClientID=100
>
> INSERT INTO Clients (ClientID, ClientName)
> VALUES (200, 'Another Company, Ltd.')
> INSERT INTO Contacts VALUES (3, 'John', 'Doe')
> INSERT INTO Contacts VALUES (4, 'Jane', 'Doe')
> INSERT INTO ClientContacts VALUES (200, 2)
> INSERT INTO ClientContacts VALUES (200, 3)
> INSERT INTO ClientContacts VALUES (200, 4)
> UPDATE Clients SET MainContactID=3 WHERE ClientID=200
> SET NOCOUNT OFF
>
> Let's suppose you want to delete the client with the ClientID=100.
> Using a simple "DELETE Clients WHERE ClientID=100" works (without any
> error): the client is deleted and it's links with the contacts, too
> (but the contacts themselves remain). If you want to also delete the
> contacts (the ones that are not linked with any other client), you can
> use the following trigger:
> CREATE TRIGGER Clients_DeleteContacts ON Clients
> INSTEAD OF DELETE
> AS
> IF @.@.ROWCOUNT>0 BEGIN
> SET NOCOUNT ON
> UPDATE Clients SET MainContactID=NULL
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> DELETE Contacts WHERE ContactID IN (
> SELECT x.ContactID FROM ClientContacts x
> WHERE x.ClientID IN (SELECT ClientID FROM deleted)
> AND NOT EXISTS (
> SELECT * FROM ClientContacts y
> WHERE x.ContactID=y.ContactID
> AND y.ClientID NOT IN (SELECT ClientID FROM deleted)
> )
> )
> DELETE Clients
> WHERE ClientID IN (SELECT ClientID FROM deleted)
> END
> Razvan
>

Circular dependencies from constraints

Hey!

I am creating a kind of file browser for an application of mine. The principle is quite straight forward. It consists of folders and files. Each folder can contain other folders and files and so on. The twitch however is that i need a special root entity called site. The site is very much alike a folder but has some other properties. The site can contain folders and files.

To achieve this ive created te following tables (truncated for clearity):

###################
# Sites #
###################
# ID [Int] #
# ... #
###################

###################
# Folders #
###################
# ID [Int] #
# SiteID [Int] #
# FolderID [Int] #
# ... #
###################

###################
# Files #
###################
# ID [Int] #
# SiteID [Int] #
# FolderID [Int] #
# ... #
###################

Both the folder table and the files table have a check constraint that ensures that either SiteID or FolderID is NULL. They WILL be part of EITHER a folder or a site. Not both!

Then i set up the foreign constraints as follows:
Folders.FolderD -> Folders.ID
Folders.SiteID -> Sites.ID
Files.FolderID -> Folders.ID
Files.SiteID -> Sites.ID

All constraints have cascade on delete and therefore the last of them cannot be created as it would be circular. (Wich it wont in this case, but theoreticaly its possible)

Iknow WHY this is rendering an error. But how can i work around it? Or would you suggest another design of the tables?

Hi Supermajs,

Firslty, I would remove the constraints.

Secondly, remove the SiteID and FolderID fields from the Folders and Files tables.

Thirdly, add the fields ParentID and ParentTypeID to the Folders and Files tables.

Then add a new table called tblParentType with the following records: -

ParentTypeID ParentType

1 Site

2 Folder

Then add a constraint between ParentType.ParentTypeID and Folders.ParentTypeID and between ParentTypeID.ParentTypeID and Files.ParentTypeID.

Now a record within Folders will look like this: -

ID ParentID ParentTypeID

1 3 1 this folder is a folder under site id 3

2 14 2 this folder is a folder under folder id 14

The same applies for the Files table.

By doing it this way, you can easily add new levels without needing extra fields that always contain NULL.

For example, you could add a new layer above site called server. The ParentType table would be as follows: -

ParentTypeID ParentType

1 Server

2 Site

3 Folder

|||

.In relational modeling it is files and association, I think you have designed flat files that could be a problem because DRI(declarative referential integrity) comes with restrictions. If you have 50 files that are associated they belong together that is how you can start with 100 files and end up with 5 tables. Try the Normalization tutorial and free data models to clean up your design and post again so I can help you with the DRI Cascade operation because it comes with fixed requirement of if A references B then B must exist. Hope this helps

http://www.utexas.edu/its/windows/database/datamodeling/rm/rm7.html

http://www.databaseanswers.org/data_models/