Mysql的Rownum使用示例

1，显示当前查询结果的行号

SELECT 
  @rownum := @rownum +1 AS rownum,
  e.*
FROM
  (SELECT 
    @rownum := 0) r,
  employee e 

显示结果如下：

2，按部门分组并按年龄降序排序并显示排名

SELECT 
  IF(@dept = e.deptNo,@rank := @rank +1,@rank := 1) AS rank,
  @dept := e.deptNo,
  e.*
FROM
  (SELECT 
    @deptno := NULL,@rank := 0) r,
  employee e 
  ORDER BY e.deptNo ASC,e.age DESC

查询结果如下

3，批量插入值，并保证值自增（主键列没有自增序列）

INSERT INTO employee(id,NAME,age,deptNo)
SELECT 
  t.id,t.name,t.age,t.deptNo
 FROM (
	SELECT 
	  @rownum := @rownum + 1,
	  (SELECT MAX(e1.id) FROM employee e1) + @rownum AS id,
	  CONCAT('姓名', @ROWNUM) AS NAME,
	  @rownum * 10 AS age,
	  30 AS deptNo
	FROM
	  (SELECT 
	    @rownum := 0) r,
	  employee e 
	WHERE e.deptno = 20 
) t

插入后，查询结果如下