ORA-01427: single-row subquery returns more than one row

The ORA-01427 is a straightforward query error in Oracle. The cause of the error is a subquery returning more than one row of information.

Try  the following SQL statement:

SELECT *

FROM employers

WHERE client_id = (SELECT client_id

         FROM clients

         WHERE clients_name = ‘Walmart’) ;

If more than one instance in the client’s table of the clients_name ‘Walmart’ existed, the following would be prompted:

ORA-01427: single-row subquery returns more than one row

You can then correct the statement by utilizing an IN condition, which is used to reduce the need for multiple OR conditions in SELECT statements:

SELECT *

FROM employers

WHERE client_id IN (SELECT client_id

      FROM clients

      WHERE clients_name = ‘Walmart’) ;

This will eliminate the ORA-01427 error message from occurring.