Oracle Error QSM-02150: select lists must be identical across the UNION operator

Oracle Error Message

QSM-02150: select lists must be identical across the UNION operator

Reason for the Error

You have specified a materialized view using the UNION operator and the respective queries on each side of the UNION operator do not have the same select list. The RELATED_NAME column shows the alias of the first different select list item. The RELATED_NUM column shows the offset from the SELECT keyword to the start of this select list item.

Solution

Restructure the materialized view query such that the respective sides of the UNION operator have identical select lists.