오라클에는 NULLS FIRST, NULLS LAST 구문이 있습니다.
PostgreSQL 에도 위 구문을 그대로 사용할수 있습니다.
아래 결과를 살펴 볼까요?
scott@[local]:5432 scottdb#SQL> select * from emp order by comm; -- 널아닌 값이 먼저 보입니다.
empno | ename | job | mgr | hiredate | sal | comm | deptno
-------+--------+-----------+------+------------+------+------+--------
7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500 | 0 | 30
7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600 | 300 | 30
7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250 | 500 | 30
7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250 | 1400 | 30
7788 | SCOTT | ANALYST | 7566 | 1982-12-09 | 3000 | NULL | 20
7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000 | NULL | 10
7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100 | NULL | 20
7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950 | NULL | 30
7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000 | NULL | 20
7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800 | NULL | 20
7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300 | NULL | 10
7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975 | NULL | 20
7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850 | NULL | 30
7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450 | NULL | 10
-- NULLS LAST 를 안붙였을때와 결과는 동일합니다.
scott@[local]:5432 scottdb#SQL> select * from emp order by comm nulls last;
empno | ename | job | mgr | hiredate | sal | comm | deptno
-------+--------+-----------+------+------------+------+------+--------
7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500 | 0 | 30
7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600 | 300 | 30
7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250 | 500 | 30
7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250 | 1400 | 30
7788 | SCOTT | ANALYST | 7566 | 1982-12-09 | 3000 | NULL | 20
7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000 | NULL | 10
7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100 | NULL | 20
7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950 | NULL | 30
7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000 | NULL | 20
7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800 | NULL | 20
7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300 | NULL | 10
7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975 | NULL | 20
7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850 | NULL | 30
7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450 | NULL | 10
-- 널값이 먼저 보이네요
scott@[local]:5432 scottdb#SQL> select * from emp order by comm nulls first;
empno | ename | job | mgr | hiredate | sal | comm | deptno
-------+--------+-----------+------+------------+------+------+--------
7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300 | NULL | 10
7876 | ADAMS | CLERK | 7788 | 1983-01-12 | 1100 | NULL | 20
7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950 | NULL | 30
7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000 | NULL | 20
7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800 | NULL | 20
7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975 | NULL | 20
7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850 | NULL | 30
7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450 | NULL | 10
7788 | SCOTT | ANALYST | 7566 | 1982-12-09 | 3000 | NULL | 20
7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000 | NULL | 10
7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500 | 0 | 30
7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600 | 300 | 30
7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250 | 500 | 30
7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250 | 1400 | 30
scott@[local]:5432 scottdb#SQL>
