Restrictions When Using the Single-Column Constraint Format

When you use the single-column constraint format to define a check constraint, the check constraint cannot depend on values in other columns of the table. The following example creates the my_accounts table that has two columns with check constraints, each in the single-column constraint format:

CREATE TABLE my_accounts (
   chk_id   SERIAL PRIMARY KEY,
   acct1    MONEY CHECK (acct1 BETWEEN 0 AND 99999),
   acct2    MONEY CHECK (acct2 BETWEEN 0 AND 99999))

Both acct1 and acct2 are columns of MONEY data type whose values must be between 0 and 99999. If, however, you want to test that acct1 has a larger balance than acct2, you cannot use the single-column constraint format. To create a constraint that checks values in more than one column, you must use the Multiple-Column Constraint Format.

Constraint Definition

Constraint Definition:
 
|--+------------------------+----------------------------------->
   '-CONSTRAINT--constraint-'
 
>--+-----------------------------------------+------------------|
   |  (1)   .-ENABLED----------------------. |
   '--------+------------------------------+-'
            +-DISABLED---------------------+
            |            .-WITHOUT ERROR-. |
            '-FILTERING--+-WITH ERROR----+-'