Question

I need to surround the following sql script with an if statment that checks the existence of one table. There’s a lot more fields to the statement but the snippet below should be enough to get the idea.

If I surround this whole batch with an if statement it doesn’t like that i have GOs between if statments. If i take out the GOs it complains about TMP_FIELD being an invalid column.

What are some ways to do this the right way? All i’m doing is taking a bunch of fields and changing from varchar to datetime. This is part of a setup.exe file so I just need it to run once and not for future upgrades. The way I determine that is if a certain table exists then don’t run the script.

IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  ALTER TABLE MY_TABLE ADD TMP_FIELD datetime
GO
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  UPDATE MY_TABLE SET TMP_FIELD = modifiedDate
GO
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  ALTER TABLE MY_TABLE DROP COLUMN modifiedDate
GO
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  ALTER TABLE MY_TABLE ADD modifiedDate datetime
GO
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  UPDATE MY_TABLE SET modifiedDate = TMP_FIELD
GO
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id(N'MY_TABLE') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
  ALTER TABLE MY_TABLE DROP COLUMN TMP_FIELD
GO

Answer 1

You don’t really need to do all that gymnastic for changing the type of a column, do you?

create table MY_TABLE (
    modifiedDate varchar(20)
)
go

insert MY_TABLE (modifiedDate) values ('2012-10-20 17:50:41')
go

select * from MY_TABLE
go

alter table MY_TABLE alter column modifiedDate datetime
go

select * from MY_TABLE
go

drop table MY_TABLE
go

So, I would write your statement like this:

if exists (select table_name from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'MY_TABLE')
begin
  alter table MY_TABLE alter column modifiedDate datetime
end