mysql怎么分析函数row

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共2个回答

热心网友

第一种方法：
select (@i:=@i+1) as i,table_name.* from table_name,(select @i:=0) as it
第二种方法：
set @rownum=0;
select @rownum:=@rownum+1 as rownum, t.username from auth_user t limit 1,5;

热心网友

一直以来，MySQL 只有针对聚合函数的汇总类功能，比如MAX, AVG 等，没有从 SQL 层针对聚合类每组展开处理的功能。不过 MySQL 开放了 UDF 接口，可以用 C 来自己写UDF，这个就增加了功能行难度。

这种针对每组展开处理的功能就叫窗口函数，有的数据库叫分析函数。

在 MySQL 8.0 之前，我们想要得到这样的结果，就得用以下几种方法来实现：

1. session 变量

2. group_concat 函数组合

3. 自己写 store routines

接下来我们用经典的学生/课程/成绩来做窗口函数演示

准备

学生表

mysql> show create table student \G*************************** 1. row *************************** Table: studentCreate Table: CREATE TABLE student ( sid int(10) unsigned NOT NULL, sname varchar() DEFAULT NULL, PRIMARY KEY (sid)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)

课程表

mysql> show create table course\G*************************** 1. row *************************** Table: courseCreate Table: CREATE TABLE `course` ( `cid` int(10) unsigned NOT NULL, `cname` varchar() DEFAULT NULL, PRIMARY KEY (`cid`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)

成绩表

mysql> show create table score\G*************************** 1. row *************************** Table: scoreCreate Table: CREATE TABLE `score` ( `sid` int(10) unsigned NOT NULL, `cid` int(10) unsigned NOT NULL, `score` tinyint(3) unsigned DEFAULT NULL, PRIMARY KEY (`sid`,`cid`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)

测试数据

mysql> select * from student;

+-----------+--------------+

| sid | sname |

+-----------+--------------+

| 201910001 | 张三 |

| 201910002 | 李四 |

| 201910003 | 武松 |

| 201910004 | 潘金莲 |

| 201910005 | 菠菜 |

| 201910006 | 杨发财 |

| 201910007 | 欧阳修 |

| 201910008 | 郭靖 |

| 201910009 | 黄蓉 |

| 201910010 | 东方不败 |

+-----------+--------------+

10 rows in set (0.00 sec)

mysql> select * from score;;

+-----------+----------+-------+

| sid | cid | score |

+-----------+----------+-------+

| 201910001 | 20192001 | 50 |

| 201910001 | 20192002 | 88 |

| 201910001 | 20192003 | 54 |

| 201910001 | 20192004 | 43 |

| 201910001 | 20192005 | |

| 201910002 | 20192001 | 79 |

| 201910002 | 20192002 | 97 |

| 201910002 | 20192003 | 82 |

| 201910002 | 20192004 | 85 |

| 201910002 | 20192005 | 80 |

| 201910003 | 20192001 | 48 |

| 201910003 | 20192002 | 98 |

| 201910003 | 20192003 | 47 |

| 201910003 | 20192004 | 41 |

| 201910003 | 20192005 | 34 |

| 201910004 | 20192001 | 81 |

| 201910004 | 20192002 | 69 |

| 201910004 | 20192003 | 67 |

| 201910004 | 20192004 | 99 |

| 201910004 | 20192005 | 61 |

| 201910005 | 20192001 | 40 |

| 201910005 | 20192002 | 52 |

| 201910005 | 20192003 | 39 |

| 201910005 | 20192004 | 74 |

| 201910005 | 20192005 | 86 |

| 201910006 | 20192001 | 42 |

| 201910006 | 20192002 | 52 |

| 201910006 | 20192003 | 36 |

| 201910006 | 20192004 | 58 |

| 201910006 | 20192005 | 84 |

| 201910007 | 20192001 | 79 |

| 201910007 | 20192002 | 43 |

| 201910007 | 20192003 | 79 |

| 201910007 | 20192004 | 98 |

| 201910007 | 20192005 | 88 |

| 201910008 | 20192001 | 45 |

| 201910008 | 20192002 | 65 |

| 201910008 | 20192003 | 90 |

| 201910008 | 20192004 | |

| 201910008 | 20192005 | 74 |

| 201910009 | 20192001 | 73 |

| 201910009 | 20192002 | 42 |

| 201910009 | 20192003 | 95 |

| 201910009 | 20192004 | 46 |

| 201910009 | 20192005 | 45 |

| 201910010 | 20192001 | 58 |

| 201910010 | 20192002 | 52 |

| 201910010 | 20192003 | 55 |

| 201910010 | 20192004 | 87 |

| 201910010 | 20192005 | 36 |

+-----------+----------+-------+

50 rows in set (0.00 sec)

mysql> select * from course;

+----------+------------+

| cid | cname |

+----------+------------+

| 20192001 | mysql |

| 20192002 | oracle |

| 20192003 | postgresql |

| 20192004 | mongodb |

| 20192005 | dble |

+----------+------------+

5 rows in set (0.00 sec)

MySQL 8.0 之前

比如我们求成绩排名前三的学生排名，我来举个用 session 变量和 group_concat 函数来分别实现的例子：

session 变量方式

每组开始赋一个初始值序号和初始分组字段。

SELECT

b.cname,

a.sname,

c.score, c.ranking_score

FROM

student a,

course b,

(

SELECT

c.*,

IF(

@cid = c.cid,

@rn := @rn + 1,

@rn := 1

) AS ranking_score,

@cid := c.cid AS tmpcid

FROM

(

SELECT

FROM

score

ORDER BY cid,

score DESC

) c,

(

SELECT

@rn := 0 rn,

@cid := ''

) initialize_table

) c

WHERE a.sid = c.sid

AND b.cid = c.cid

AND c.ranking_score <= 3

ORDER BY b.cname,c.ranking_score;

+------------+-----------+-------+---------------+

+------------+-----------+-------+---------------+

| dble | 张三 | | 1 |

| dble | 欧阳修 | 88 | 2 |

| dble | 菠菜 | 86 | 3 |

| mongodb | 潘金莲 | 99 | 1 |

| mongodb | 欧阳修 | 98 | 2 |

| mongodb | 郭靖 | | 3 |

| mysql | 李四 | 100 | 1 |

| mysql | 潘金莲 | 81 | 2 |

| mysql | 欧阳修 | 79 | 3 |

| oracle | 武松 | 98 | 1 |

| oracle | 李四 | 97 | 2 |

| oracle | 张三 | 88 | 3 |

| postgresql | 黄蓉 | 95 | 1 |

| postgresql | 郭靖 | 90 | 2 |

| postgresql | 李四 | 82 | 3 |

+------------+-----------+-------+---------------+

15 rows in set, 5 warnings (0.01 sec)

group_concat 函数方式

利用 findinset 内置函数来返回下标作为序号使用。

SELECT

FROM

(

SELECT

b.cname,

a.sname,

c.score,

FIND_IN_SET(c.score, d.gp) score_ranking

FROM

student a,

course b,

score c,

(

SELECT

cid,

GROUP_CONCAT(

score

ORDER BY score DESC SEPARATOR ','

) gp

FROM

score

GROUP BY cid

ORDER BY score DESC

) d

WHERE a.sid = c.sid

AND b.cid = c.cid

AND c.cid = d.cid

ORDER BY d.cid,

score_ranking

) ytt

WHERE score_ranking <= 3；

+------------+-----------+-------+---------------+

+------------+-----------+-------+---------------+

| dble | 张三 | | 1 |

| dble | 欧阳修 | 88 | 2 |

| dble | 菠菜 | 86 | 3 |

| mongodb | 潘金莲 | 99 | 1 |

| mongodb | 欧阳修 | 98 | 2 |

| mongodb | 郭靖 | | 3 |

| mysql | 李四 | 100 | 1 |

| mysql | 潘金莲 | 81 | 2 |

| mysql | 欧阳修 | 79 | 3 |

| oracle | 武松 | 98 | 1 |

| oracle | 李四 | 97 | 2 |

| oracle | 张三 | 88 | 3 |

| postgresql | 黄蓉 | 95 | 1 |

| postgresql | 郭靖 | 90 | 2 |

| postgresql | 李四 | 82 | 3 |

+------------+-----------+-------+---------------+

15 rows in set (0.00 sec)

MySQL 8.0 窗口函数

MySQL 8.0 后提供了原生的窗口函数支持，语法和大多数数据库一样，比如还是之前的例子：

用 row_number() over () 直接来检索排名。

mysql>

SELECT

FROM

(

SELECT

b.cname,

a.sname,

c.score,

row_number() over (

PARTITION BY b.cname

ORDER BY c.score DESC

) score_rank

FROM

student AS a,

course AS b,

score AS c

WHERE a.sid = c.sid

AND b.cid = c.cid

) ytt

WHERE score_rank <= 3;

+------------+-----------+-------+------------+

+------------+-----------+-------+------------+

| dble | 张三 | | 1 |

| dble | 欧阳修 | 88 | 2 |

| dble | 菠菜 | 86 | 3 |

| mongodb | 潘金莲 | 99 | 1 |

| mongodb | 欧阳修 | 98 | 2 |

| mongodb | 郭靖 | | 3 |

| mysql | 李四 | 100 | 1 |

| mysql | 潘金莲 | 81 | 2 |

| mysql | 欧阳修 | 79 | 3 |

| oracle | 武松 | 98 | 1 |

| oracle | 李四 | 97 | 2 |

| oracle | 张三 | 88 | 3 |

| postgresql | 黄蓉 | 95 | 1 |

| postgresql | 郭靖 | 90 | 2 |

| postgresql | 李四 | 82 | 3 |

+------------+-----------+-------+------------+

15 rows in set (0.00 sec)

那我们再找出课程 MySQL 和 DBLE 里不及格的倒数前两名学生名单。

mysql>

SELECT

FROM

(

SELECT

b.cname,

a.sname,

c.score,

row_number () over (

PARTITION BY b.cid

ORDER BY c.score ASC

) score_ranking

FROM

student AS a,

course AS b,

score AS c

WHERE a.sid = c.sid

AND b.cid = c.cid

AND b.cid IN (20192005, 20192001)

AND c.score < 60

) ytt

WHERE score_ranking < 3;

+-------+--------------+-------+---------------+

+-------+--------------+-------+---------------+

| mysql | 菠菜 | 40 | 1 |

| mysql | 杨发财 | 42 | 2 |

| dble | 武松 | 34 | 1 |

| dble | 东方不败 | 36 | 2 |

+-------+--------------+-------+---------------+

4 rows in set (0.00 sec)

到此为止，我们只是演示了row_number() over() 函数的使用方法，其他的函数有兴趣的朋友可以自己体验体验，方法都差不多。

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mysql怎么分析函数row