Sub queries in check constraint

问题:

I have table designed in SQL-Server 2008 R2.

I have a column in that table which needs to be checked against another table when data is inserting.

ALTER TABLE Table1         WITH CHECK ADD CONSTRAINT CK_Code         CHECK (MyField in (Select Field From Table2)) 

This cause an error

Sub-queries are not allowed in this context. Only scalar expressions are allowed.

I have looked at this question about Check Constraint - Subqueries are not allowed in this context.

Is there any way of achieving this without using a trigger?

回答1:

Note, what you really want is a foreign key constraint. That said, to get a "query" into a check you can write a function that contains the query and outputs a scalar value, then use that function in the check constraint.

CREATE FUNCTION myFunction (     @field DATATYPE(?) ) RETURNS VARCHAR(5) AS BEGIN     IF EXISTS (SELECT* FROM Table2 WHERE MYFIELD = @field)         return 'True'     return 'False' END 

Something like that. Not tested.

Then you can add it to your check like so

ALTER TABLE Table1     WITH CHECK ADD CONSTRAINT CK_Code     CHECK (myFunction(MYFIELD) = 'True') 

回答2:

You can't have sub queries inside check constraints. What you can do is use a UDF that returns a scalar value inside the check constraint.

Step 1: Create the table

USE CTBX GO  CREATE TABLE RawMaterialByGender  ( RMGID int primary key identity(1,1), RMID smallint foreign key references RawMaterialMaster(RMID), LeveLMasterID smallint foreign key references LevelMaster(LevelTextID), IsDeleted bit ) 

Step 2 : Create the UDF that returns a scalar

Create FUNCTION [dbo].[IsValidLevelMasterGender](@LevelMasterID smallint)      RETURNS bit     AS     BEGIN      DECLARE @count smallint;      DECLARE @return bit;       SELECT @count = count(LevelTextID)            FROM [LevelMaster]      WHERE LevelCategoryID = 3 AND IsActive = 1 AND LevelTextID=@LevelMasterID       IF(@count = 0)      SET @return = 'false';      ELSE      SET @return = 'true';       RETURN @return;      END;     GO 

Step 3 : Alter table to add the CHECK constraint

ALTER TABLE RawMaterialByGender  ADD CONSTRAINT check_LevelMasterID CHECK (dbo.IsValidLevelMasterGender(LeveLMasterID) = 'true') 

回答3:

ALTER TABLE Table1 ADD CONSTRAINT FK_Table1_Code FOREIGN KEY (MyField) REFERENCES Table2 (Field) ; 

Ref: http://msdn.microsoft.com/en-us/library/ms190273.aspx
Note: I haven't checked the above for syntax.

回答4:

First of all in your example you clearly need FK Constraint.

Another posibility is to use view with WITH CHECK OPTION and give access to user through it:

CREATE TABLE Table1(i INT PRIMARY KEY, CK_Code CHAR(1)); CREATE TABLE Table2(Field CHAR(1)); INSERT INTO Table2(Field) VALUES ('A'),('B'), ('C'); GO  CREATE VIEW v_Table1 AS SELECT * FROM Table1 WHERE CK_code IN (SELECT Field FROM Table2)  -- here goes your subquery check WITH CHECK OPTION; 

When you try to insert data that violates your "constraint" like:

INSERT INTO v_Table1(i, CK_Code) VALUES(10, 'D'); 

You will get:

The attempted insert or update failed because the target view either specifies WITH CHECK OPTION or spans a view that specifies WITH CHECK OPTION and one or more rows resulting from the operation did not qualify under the CHECK OPTION constraint.

The statement has been terminated.

LiveDemo

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