SQL IF statement is being ignored

Question

I have a long script and I like to be able to just run the whole file when I need to and not worry about if parts of it have already ran. But the script below is giving me probl

Answer 1

Martin was definitely onto something. The stuff inside the IF is being treated by the parser at parse time and ignoring whether your IF will pan out. This is the same reason you can't do:

IF 1 = 1
  CREATE TABLE #x(a INT);
ELSE
  CREATE TABLE #x(b INT);

One workaround would be to use dynamic SQL:

IF EXISTS ...
BEGIN
  BEGIN TRANSACTION;

  DECLARE @sql NVARCHAR(MAX);

  SET @sql = N'
        DELETE FROM [dbo].[Notes]
        WHERE [EntityId] IS NULL 
        AND [EntityType] IS NULL
        --Delete notes where the corresponding contact or account has been deleted.
        OR [ID] IN (9788, 10684, 10393, 10718, 10719)

        --Populate new columns with all existing data
        UPDATE [dbo].[Notes]
        SET [AccountId] = [EntityId]
        WHERE [EntityType] = 1

        UPDATE [dbo].[Notes]
        SET [ContactId] = [EntityId]
        WHERE [EntityType] = 2

        --Delete EntityId and EntityType columns from the Notes table
        ALTER TABLE [dbo].[Notes]
        DROP COLUMN [EntityId], [EntityType]';

    EXEC sp_executesql @sql;

    COMMIT TRANSACTION;
END

But you still should be sure that both columns are there.