1 UPDATE PM_ASSIGNMENTS
2 SET PM_ASSIGNMENTS.JOB_TYPE_CODE = (SELECT PM_TASK_DETAILS.JOB_TYPE_CODE
3 FROM PM_ASSIGNMENTS, PM_TASK_DETAILS
4 WHERE ((PM_ASSIGNMENTS.TASK_NUMBER) = (PM_TASK_DETAILS.TASK_NUMBER))
5* AND (PM_ASSIGNMENTS.TASK_NUMBER = '1000'))
SQL> /
SET PM_ASSIGNMENTS.JOB_TYPE_CODE = (SELECT PM_TASK_DETAILS.JOB_TYPE_CODE
*
ERROR at line 2:
ORA-01427: single-row subquery returns more than one row

the sub-query is returning more than one row for the given condition.

either group-by them, or give all user-key conditions.

regards,
Raghu.