How do I know if a field exists?

IF NOT EXISTS
   (SELECT c.*
    FROM syscolumns c
       JOIN sysobjects o ON c.id = o.id
    WHERE o.name = 'TABLE_1'
       AND c.name = 'FIELD_1')
   BEGIN
      ALTER TABLE [dbo].[TABLE_1] ADD [FIELD_1] ....

IF NOT EXISTS(
   SELECT *
   FROM sysobjects
   INNER JOIN syscolumns
      ON sysobjects.id = syscolumns.id
   WHERE syscolumns.name = 'Field_1'
      AND sysobjects.name = 'Table_1'
) THEN ALTER...

A field in what?
Do you mean a table column?
Some value in a table column?
A field in a report?
 

Try this too
--IF (NOT(EXISTS(SELECT FIELD_1 FROM TABLE_1))) THEN ALTER ..........

IF NOT EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS WHERE COLUMN_NAME = ' Ur Field' AND TABLE_NAME = 'UrTable)'
ALTER TABLE ...

I am glad you agree with me :)

Oh sorry aceperkins , i didn't find your post

No problem.