Defining Check Constraints Across Columns

When you use the multiple-column constraint format to define check constraints, a check constraint can apply to more than one column in the same table. (You cannot, however, create a check constraint whose condition uses a value from a column in another table.)

This example compares two columns, acct1 and acct2, in the new table:

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

In this example, the acct1 column must be greater than the acct2 column, or the insert or update fails.