SQL Constraint conditional Check: if column0 is null, column1 is not null and vice versa

Question

I have this question around SQL constraints, in order to achieve following behavior:

TableA has two columns column0 and column1, which only one can be NULL on data entry: eg: if column0 is null, column1 can't be null if column1 is null, column0 can't be null

To achieve this, I've build following SQL constraints:

CONSTRAINT column01_not_null_chk
CHECK (
  ( column0 IS NOT NULL
  AND column1 IS NULL )
OR
  ( column1 IS NOT NULL
  AND column0 IS NULL ) )

is this correct to achieve my behavior? Because all SQL are rejected because of this constraint

Answer 1

The condition you described means that at least one of them has to have value. So your constraint should be corrected to:

CONSTRAINT column01_not_null_chk
CHECK (column0 IS NOT NULL OR column1 IS NOT NULL)

Answer 2

Seems to work fine on SQL Server:

create table t (
     column0 int null
   , column1 int null
, CONSTRAINT column01_not_null_chk
CHECK (
  ( column0 IS NOT NULL
  AND column1 IS NULL )
OR
  ( column1 IS NOT NULL
  AND column0 IS NULL ) )
);

insert into t values (null,1),(1,null);

select * from t;
--insert into t values (null,null) /* fail */
--insert into t values (1,1) /* fail */

rextester demo : http://rextester.com/OQZNE39497

returns:

+---------+---------+
| column0 | column1 |
+---------+---------+
| NULL    | 1       |
| 1       | NULL    |
+---------+---------+