执行函数“子查询必须仅返回一列”时出现错误

Question

我收到错误消息，因为“子查询必须仅返回一列”。因为我每个部门都有更多的员工。告诉我解决此问题的解决方案

CREATE OR REPLACE FUNCTION dept_emp()
    RETURNS TEXT AS
    $$
    DECLARE
    cur_dept CURSOR FOR SELECT dept_name FROM dept;
    cur_emp CURSOR FOR SELECT employee_id,dob,department FROM emp;
    d RECORD;
    e RECORD;
    BEGIN
    FOR d IN SELECT dept_name FROM dept
    LOOP
        FOR e IN SELECT employee_id,dob,department FROM emp
            LOOP
                RAISE NOTICE 'Department: %',d.dept_name;
                RETURN (SELECT employee_id,dob FROM emp WHERE d.dept_name=e.department); 
            END LOOP;
    END LOOP;
    END;
    $$ LANGUAGE 'plpgsql';