Question

I am trying to make a stored procedure to clean constraints from a table.

I have some trouble checking is the is null or empty, also to check is the table exist is there a way more elegant than nest a if to check if the table exists and the parameter isn’t null or empty?

This is for SQL Server 2008 R2.

ALTER PROCEDURE [dbo].[sp_quitarConstrain](@table NVARCHAR(50))
AS
DECLARE @database NVARCHAR(50)
DECLARE @sql NVARCHAR(255)
SET @database = 'table'

IF((COALESCE(@table,'') <> '') OR (@table IS NULL))
    BEGIN
        PRINT 'Necesitas dar una tabla valida'
        RETURN 
    END
ELSE
    BEGIN
        WHILE EXISTS(SELECT * FROM sys.foreign_keys WHERE referenced_object_id = object_id(+ @table))
        BEGIN
            SELECT    @sql = 'ALTER TABLE ' + OBJECT_NAME(parent_object_id) + ' DROP CONSTRAINT ' + name 
            FROM    sys.foreign_keys 
            WHERE    referenced_object_id = object_id(@table)

            EXEC    sp_executesql @sql
        END
    END

Answer 1

Your Stored Proc does work, with only minor changes – e.g. (COALESCE(@table,'') <> '') should be (COALESCE(@table,'') = '')

ALTER PROCEDURE [dbo].[sp_quitarConstrain](@table NVARCHAR(50))
AS
    DECLARE @sql NVARCHAR(255)

    IF((COALESCE(@table,'') = '') OR (@table IS NULL))
        BEGIN
            PRINT 'Necesitas dar una tabla valida'
            RETURN 
        END
    ELSE
        BEGIN
            WHILE EXISTS(SELECT * FROM sys.foreign_keys WHERE referenced_object_id = object_id(@table))
                BEGIN
                    SELECT    @sql = 'ALTER TABLE ' + OBJECT_NAME(parent_object_id) + ' DROP CONSTRAINT ' + name 
                    FROM    sys.foreign_keys 
                    WHERE    referenced_object_id = object_id(@table)
                    EXEC    sp_executesql @sql
                END
        END

If you aren’t too picky about schemas, you could check for the table like so:

IF NOT EXISTS(SELECT 1 FROM sys.tables WHERE name=@table)
    BEGIN
        PRINT 'Necesitas dar una tabla valida'
        RETURN 
    END