Drop column and all dependent objects using data definition language

Question

I need to remove a column from a table, but when I try to remove it:

The object 'object_name' is dependent on column 'column_name'.

ALTER TABLE DROP COLUMN column_name failed because one or more objects access this column.

I can look for the dependency in the system tables and remove it manually, but I need to do a migration (using SQL DDL) so all others members of the team just do the update, run the migration and don´t have to mess up up system objects.

Answer 1

Try this code:

Declare @TABLENAME varchar(max), @COLUMN varchar(max)
SET @TABLENAME = 'YOURTableName'
SET @COLUMN = 'YOURColumnName'
Declare @CONSTRAINT varchar(max)
                    set @CONSTRAINT ='ALTER TABLE '+@TABLENAME+' DROP CONSTRAINT '
                    set @CONSTRAINT = @CONSTRAINT + (select SYS_OBJ.name as CONSTRAINT_NAME
                    from sysobjects SYS_OBJ
                    join syscomments SYS_COM on SYS_OBJ.id = SYS_COM.id
                    join sysobjects SYS_OBJx on SYS_OBJ.parent_obj = SYS_OBJx.id 
                    join sysconstraints SYS_CON on SYS_OBJ.id = SYS_CON.constid
                    join syscolumns SYS_COL on SYS_OBJx.id = SYS_COL.id
                    and SYS_CON.colid = SYS_COL.colid
                    where
                    SYS_OBJ.uid = user_id() and SYS_OBJ.xtype = 'D'
                    and SYS_OBJx.name=@TABLENAME and SYS_COL.name=@COLUMN)
                    exec(@CONSTRAINT)

and then run your regular alter table:

ALTER TABLE YOURTABLENAME
DROP COLUMN YOURCOLUMNNAME

With the first code you remove all the dependencies on that column and then you can remove it without problems.

EDIT - Removing Default Values Constraints:

The code above does not seems to remove DEFAULT_CONSTRAINTS so, in that case you must also use:

DECLARE @ConstraintName nvarchar(200)
SELECT @ConstraintName = Name FROM SYS.DEFAULT_CONSTRAINTS WHERE PARENT_OBJECT_ID = OBJECT_ID('__TableName__') AND PARENT_COLUMN_ID = (SELECT column_id FROM sys.columns WHERE NAME = N'__ColumnName__' AND object_id = OBJECT_ID(N'__TableName__'))
IF @ConstraintName IS NOT NULL
    EXEC('ALTER TABLE __TableName__ DROP CONSTRAINT ' + @ConstraintName)