I need a check constraint on two columns, at least one must be not null

Question

I have a table in SQL Server with two numeric columns. At least one of these numeric fields must be filled. How do I write a check constraint to verify this?

Rudie

Possible duplicate of One of the column between two columns should be NOT NULL. How to enforce it in schema? – Kristofor

@Kristofor not duplicate as this question is about 'at least one of two' and that one is about 'only one of two' – Elgon

Answer 1

This can be done with a check constraint that verifies null value and matches the result with or

create table #t (i int
               , j int
               , constraint chk_null check (i is not null or j is not null))

The following are the test cases

insert into #t values (null, null) --> error
insert into #t values (1, null) --> ok
insert into #t values (null, 1) --> ok
insert into #t values (1, 1) --> ok

Woodpecker

Answer 2

late answer, but here is a solution for Sql Server for any number of columns to check:

CONSTRAINT CK_one_is_not_null CHECK (COALESCE(col1, col2, col3) IS NOT NULL )

Elgon

This works if the columns have the same datatype. Otherwise the system will try to convert in order to check this constraint – Fuegian

ISNULL(a,b) can be used if there are two columns, but COALESCE is more general. – Equidistance

Answer 3

Another option:

CONSTRAINT at_least_one_not_null CHECK (
            COALESCE((col1)::BOOLEAN::INTEGER, 0) +
            COALESCE((col2)::BOOLEAN::INTEGER, 0) > 0
    )

Zemstvo