Why does SQL Server keep creating a DF constraint?
SqlSql ServerSql Server-2008Sql Problem Overview
I'm trying to create upgrade and backout scripts in SQL. The upgrade script adds a column like so:
IF NOT EXISTS (SELECT * FROM sys.columns WHERE Name = N'ColumnName'
AND object_id = OBJECT_ID(N'[dbo].[TableName]'))
ALTER TABLE TableName
ADD ColumnName bit NOT NULL DEFAULT(0)
The backout script removes the column like so:
IF EXISTS (SELECT * FROM sys.columns WHERE Name = N'ColumnName'
AND object_id = OBJECT_ID(N'[dbo].[TableName]'))
ALTER TABLE TableName
DROP COLUMN ColumnName
However, the backout script throws this error:
Msg 5074, Level 16, State 1, Line 5
The object 'DF__TableName__ColumnName__1BF3D5BD' is dependent on column 'ColumnName'.
Msg 4922, Level 16, State 9, Line 5
ALTER TABLE DROP COLUMN ColumnName failed because one or more objects access this column.
I know how to drop the constraint, but the constraint's name changes everytime (the suffix changes). I either need SQL Server to stop creating this randomly-named constraint OR I need to be able to remove the constraint in my script using wild-card characters, since the name changes.
Sql Solutions
Solution 1 - Sql
This is the default
constraint that is added because of the DEFAULT(0)
in your newly added column.
You can name this yourself so it has a known fixed name rather than relying on the auto name generation.
ALTER TABLE TableName
ADD ColumnName bit NOT NULL CONSTRAINT DF_Some_Fixed_Name DEFAULT(0)
Then to remove the column and constraint together
ALTER TABLE dbo.TableName
DROP CONSTRAINT DF_Some_Fixed_Name, COLUMN ColumnName
Solution 2 - Sql
Run this:
declare @name as nvarchar(255);
SELECT @name = name FROM dbo.sysobjects
WHERE name LIKE 'DF__XXX__YYY__%' and type = 'D'
IF @name IS NOT NULL BEGIN
EXEC('ALTER TABLE XXX DROP CONSTRAINT ' + @name);
END
Solution 3 - Sql
Run this if you want remove constraint:
DECLARE @tableName NVARCHAR(255) = '[INSERT]';
DECLARE @first5CharsFromColumnName NVARCHAR(255) = '[INSERT]';
DECLARE @name NVARCHAR(255);
SELECT @name = d.name FROM dbo.sysobjects d
INNER JOIN dbo.sysobjects t ON t.id = d.parent_obj
WHERE d.name LIKE '%'+@first5CharsFromColumnName+'%' AND d.type = 'D' AND t.name = @tableName
IF @name IS NOT NULL BEGIN
EXEC('ALTER TABLE '+@tableName+' DROP CONSTRAINT ' + @name);
END