mysql查詢用號,如何使用MySQL中的實用函數及查詢技巧

數據庫

錢良釵2年前17瀏覽0評論

mysql查詢用號，如何使用MySQL中的實用函數及查詢技巧？

一直以來，MySQL 只有針對聚合函數的匯總類功能，比如MAX, AVG 等，沒有從 SQL 層針對聚合類每組展開處理的功能。不過 MySQL 開放了 UDF 接口，可以用 C 來自己寫UDF，這個就增加了功能行難度。

這種針對每組展開處理的功能就叫窗口函數，有的數據庫叫分析函數。

在 MySQL 8.0 之前，我們想要得到這樣的結果，就得用以下幾種方法來實現：

1. session 變量

2. group_concat 函數組合

3. 自己寫 store routines

接下來我們用經典的學生/課程/成績來做窗口函數演示

準備

學生表

mysql> show create table student \G*************************** 1. row ***************************Table: studentCreate Table: CREATE TABLE student (sid int(10) unsigned NOT NULL,sname varchar(64) DEFAULT NULL,PRIMARY KEY (sid)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)

課程表

mysql> show create table course\G*************************** 1. row ***************************Table: courseCreate Table: CREATE TABLE `course` (`cid` int(10) unsigned NOT NULL,`cname` varchar(64) DEFAULT NULL,PRIMARY KEY (`cid`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)

成績表

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)

測試數據

mysql> select * from student;+-----------+--------------+| sid | sname |+-----------+--------------+| 201910001 | 張三 || 201910002 | 李四 || 201910003 | 武松 || 201910004 | 潘金蓮 || 201910005 | 菠菜 || 201910006 | 楊發財 || 201910007 | 歐陽修 || 201910008 | 郭靖 || 201910009 | 黃蓉 || 201910010 | 東方不敗 |+-----------+--------------+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 | 89 || 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 | 89 || 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

比如我們求成績排名前三的學生排名，我來舉個用 session 變量和 group_concat 函數來分別實現的例子：

session 變量方式

每組開始賦一個初始值序號和初始分組字段。

SELECTb.cname,a.sname,c.score, c.ranking_scoreFROMstudent a,course b,(SELECTc.*,IF(@cid = c.cid,@rn := @rn + 1,@rn := 1) AS ranking_score,@cid := c.cid AS tmpcidFROM(SELECT*FROMscoreORDER BY cid,score DESC) c,(SELECT@rn := 0 rn,@cid := '') initialize_table) cWHERE a.sid = c.sidAND b.cid = c.cidAND c.ranking_score <= 3ORDER BY b.cname,c.ranking_score;+------------+-----------+-------+---------------+| cname | sname | score | ranking_score |+------------+-----------+-------+---------------+| dble | 張三 | 89 | 1 || dble | 歐陽修 | 88 | 2 || dble | 菠菜 | 86 | 3 || mongodb | 潘金蓮 | 99 | 1 || mongodb | 歐陽修 | 98 | 2 || mongodb | 郭靖 | 89 | 3 || mysql | 李四 | 100 | 1 || mysql | 潘金蓮 | 81 | 2 || mysql | 歐陽修 | 79 | 3 || oracle | 武松 | 98 | 1 || oracle | 李四 | 97 | 2 || oracle | 張三 | 88 | 3 || postgresql | 黃蓉 | 95 | 1 || postgresql | 郭靖 | 90 | 2 || postgresql | 李四 | 82 | 3 |+------------+-----------+-------+---------------+15 rows in set, 5 warnings (0.01 sec)

group_concat 函數方式

利用 findinset 內置函數來返回下標作為序號使用。

SELECT*FROM(SELECTb.cname,a.sname,c.score,FIND_IN_SET(c.score, d.gp) score_rankingFROMstudent a,course b,score c,(SELECTcid,GROUP_CONCAT(scoreORDER BY score DESC SEPARATOR ',') gpFROMscoreGROUP BY cidORDER BY score DESC) dWHERE a.sid = c.sidAND b.cid = c.cidAND c.cid = d.cidORDER BY d.cid,score_ranking) yttWHERE score_ranking <= 3；+------------+-----------+-------+---------------+| cname | sname | score | score_ranking |+------------+-----------+-------+---------------+| dble | 張三 | 89 | 1 || dble | 歐陽修 | 88 | 2 || dble | 菠菜 | 86 | 3 || mongodb | 潘金蓮 | 99 | 1 || mongodb | 歐陽修 | 98 | 2 || mongodb | 郭靖 | 89 | 3 || mysql | 李四 | 100 | 1 || mysql | 潘金蓮 | 81 | 2 || mysql | 歐陽修 | 79 | 3 || oracle | 武松 | 98 | 1 || oracle | 李四 | 97 | 2 || oracle | 張三 | 88 | 3 || postgresql | 黃蓉 | 95 | 1 || postgresql | 郭靖 | 90 | 2 || postgresql | 李四 | 82 | 3 |+------------+-----------+-------+---------------+15 rows in set (0.00 sec)

MySQL 8.0 窗口函數

MySQL 8.0 后提供了原生的窗口函數支持，語法和大多數數據庫一樣，比如還是之前的例子：

用 row_number() over () 直接來檢索排名。

mysql>SELECT*FROM(SELECTb.cname,a.sname,c.score,row_number() over (PARTITION BY b.cnameORDER BY c.score DESC) score_rankFROMstudent AS a,course AS b,score AS cWHERE a.sid = c.sidAND b.cid = c.cid) yttWHERE score_rank <= 3;+------------+-----------+-------+------------+| cname | sname | score | score_rank |+------------+-----------+-------+------------+| dble | 張三 | 89 | 1 || dble | 歐陽修 | 88 | 2 || dble | 菠菜 | 86 | 3 || mongodb | 潘金蓮 | 99 | 1 || mongodb | 歐陽修 | 98 | 2 || mongodb | 郭靖 | 89 | 3 || mysql | 李四 | 100 | 1 || mysql | 潘金蓮 | 81 | 2 || mysql | 歐陽修 | 79 | 3 || oracle | 武松 | 98 | 1 || oracle | 李四 | 97 | 2 || oracle | 張三 | 88 | 3 || postgresql | 黃蓉 | 95 | 1 || postgresql | 郭靖 | 90 | 2 || postgresql | 李四 | 82 | 3 |+------------+-----------+-------+------------+15 rows in set (0.00 sec)

那我們再找出課程 MySQL 和 DBLE 里不及格的倒數前兩名學生名單。

mysql>SELECT*FROM(SELECTb.cname,a.sname,c.score,row_number () over (PARTITION BY b.cidORDER BY c.score ASC) score_rankingFROMstudent AS a,course AS b,score AS cWHERE a.sid = c.sidAND b.cid = c.cidAND b.cid IN (20192005, 20192001)AND c.score < 60) yttWHERE score_ranking < 3;+-------+--------------+-------+---------------+| cname | sname | score | score_ranking |+-------+--------------+-------+---------------+| mysql | 菠菜 | 40 | 1 || mysql | 楊發財 | 42 | 2 || dble | 武松 | 34 | 1 || dble | 東方不敗 | 36 | 2 |+-------+--------------+-------+---------------+4 rows in set (0.00 sec)

到此為止，我們只是演示了row_number() over() 函數的使用方法，其他的函數有興趣的朋友可以自己體驗體驗，方法都差不多。