ROW_NUMBER() partition by ;分组,组内按第二个字段排序,并赋予组内编码
SELECT deptno,ename,empno,
ROW_NUMBER() OVER(partition by deptno ORDER BY empno) AS emp_id
FROM emp;
SELECT deptno,ename,empno,
ROW_NUMBER() OVER(partition by deptno ORDER BY empno) AS emp_id
FROM emp;