Question

Could anyone please let me know if there is a way to programatically determine if a Micorosft SQL Server database table field has a NULL or NOT NULL constraint in place? I need this so that I can deploy a patch that is safe to be re-runnable. So I’m after something like this (conceptual/pseudo-code):

IF (my_table COLUMN end_date HAS CONSTRAINT OF 'NOT NULL') ALTER TABLE my_table ALTER COLUMN end_date DATETIME NULL

So I want to change my_table.end_date from ‘NOT NULL’ to ‘NULL’ if it hasn’t already been changed. I’m just unsure of what the part in the brackets should be.

I know how to interrogate dbo.sysobjects for things like existing fields, existing foreign key constraints and the like (there are a few threads already on that), but I’m just not sure how to check specifically for a NULL/NOT NULL field constraint. Any help would be much appreciated.

Answer 1

You can look at INFORMATION_SCHEMA.COLUMNS:

if (select IS_NULLABLE from INFORMATION_SCHEMA.COLUMNS 
    where TABLE_NAME='my_table' and COLUMN_NAME='end_date') = 'NO' 
begin
    ALTER TABLE my_table ALTER COLUMN end_date DATETIME NULL
end