PLS-00398：wrong number of columns in UNION, INTERSECT, or MINUS expression

错误原因：The SELECT clauses to the left and right of a UNION, INTERSECT, or MINUS expression do not select the same number of columns. For example, the following statement is faulty because the select lists do not contain the same number of items: CURSOR my_cur IS SELECT ename FROM emp INTERSECT SELECT ename, empno FROM emp;