MySQL] 行列转换变化各种方法实现总结（行变列报表统计、列变行数据记录统计等）

「爱情、让人受尽委屈。」 2022-07-12 09:20 63阅读 0赞

前言：

行列变化，最难的就是将多个列变成多行，使用的比较多的是统计学中行变列，列变行，没有找到现成的函数或者语句，所以自己写了存储过程，使用动态 sql 来实现，应用业务场景，用户每个月都有使用记录数录入一张表，一个月一个字段，所以表的字段是动态增长的，现在需要实时统计当前用户使用的总数量，如果你知道有多少个字段，那么可以用 select c1+c2+c3+…. From tbname where tid=’111’; 来实现，但是关键是这个都是动态的，所以在应用程序端来实现确实不适宜，可以放在数据库后台在存储过程里实现。

而且在行变成列中，如果要写单个 sql 来实现，列的数目就需要写死，因为如果不知道要展示成多少列的话，就需要用动态变量，而一条 sql 里面无法使用动态变量。但是可以使用 sql

块来实现动态的效果。

## 一，列变成行例子演示 ##

### 1 ，准备测试数据 ###

这是基础数据表，里面有多个字段wm201403…… ，现在需要把N 个这样的列变成行数据。

USE csdn;
    DROP TABLE IF EXISTS flow_table;
    CREATE TABLE `flow_table` (
      `ID` INT(11) NOT NULL AUTO_INCREMENT,
      `Number` BIGINT(11) NOT NULL,
      `City` VARCHAR(10) NOT NULL,
      `wm201403` DECIMAL(7,2) DEFAULT NULL,
      `wm201404` DECIMAL(7,2) DEFAULT NULL,
      `wm201405` DECIMAL(7,2) DEFAULT NULL,
      `wm201406` DECIMAL(7,2) DEFAULT NULL,
      `wm201407` DECIMAL(7,2) DEFAULT NULL,
      `wm201408` DECIMAL(7,2) DEFAULT NULL,
      PRIMARY KEY (`ID`,`Number`)
    ) ENGINE=INNODB   DEFAULT CHARSET=utf8;

录入一批测试数据：

INSERT INTO flow_table(Number,City,wm201403,wm201404,wm201405,wm201406,wm201407,wm201408)SELECT 1,'shanghai',100.2,180.4,141,164,124,127;
    INSERT INTO flow_table(Number,City,wm201403,wm201404,wm201405,wm201406,wm201407,wm201408)SELECT 2,'shanghai',110.23,180.34,141.23,104.78,124.67,127.45;
    INSERT INTO flow_table(Number,City,wm201403,wm201404,wm201405,wm201406,wm201407,wm201408)SELECT 3,'beijing',123.23,110.34,131.33,154.58,154.67,167.45;
    INSERT INTO flow_table(Number,City,wm201403,wm201404,wm201405,wm201406,wm201407,wm201408)SELECT 4,'hangzhou',0,110.34,131.33,154.58,154.67,0;
    INSERT INTO flow_table(Number,City,wm201405,wm201406,wm201407,wm201408)SELECT 5,'hangzhou',131.33,154.58,154.67,0;

需要达到的统计效果是：

\+--------+-----------+

| Number | total\_num |

\+--------+-----------+

|      1 |    836.60 |

|      2 |    788.70 |

|      3 |    841.60 |

|      4 |    550.92 |

|      5 |    440.58 |

\+--------+-----------+

5 rows in set (0.00 sec)

### 2 ，存储过程遍历： ###

这个存储过程建立了 2 张临时表，查询测试表数据形成游标，遍历游标根据主键 Number 来调用 pro\_flow\_modify 存储过程进行行列变化。代码如下：

DELIMITER $$
    DROP PROCEDURE IF EXISTS csdn.`proc_all_changes`$$
    CREATE PROCEDURE csdn.proc_all_changes()
    BEGIN
        DECLARE v_number BIGINT;
        DECLARE v_city VARCHAR(10);
        DECLARE _done INT DEFAULT 0; 
        
        /*定义游标*/
        DECLARE cur_all CURSOR FOR SELECT Number,City FROM csdn.`flow_table`;
        /**这里如果需要定义下当NOT FOUND的时候，EXIT退出游标遍历，不然如果设置成CONTINUE会一直执行下去。*/
        DECLARE EXIT HANDLER FOR NOT FOUND BEGIN SET _done=1;END;      
        
    	/*建立临时表，存放所有字段的临时表*/
    	DROP TABLE IF EXISTS flow_n_columns;
    	CREATE TABLE `flow_n_columns` (
    	  `column_name` VARCHAR(10) NOT NULL
    	) ENGINE=INNODB DEFAULT CHARSET=utf8;
    
    	/*存放最终变成行的数据表*/
    	DROP TABLE IF EXISTS flow_tmp;
    	CREATE TABLE `flow_tmp` (
    	  `Number` INT(11) DEFAULT NULL,
    	  `City` VARCHAR(10) DEFAULT NULL,
    	  `wm_str` VARCHAR(10) DEFAULT NULL,
    	  `Wm` DECIMAL(7,2) DEFAULT NULL
    	) ENGINE=INNODB DEFAULT CHARSET=utf8;
    
        OPEN cur_all;
        REPEAT
    	 FETCH cur_all INTO v_number, v_city;
    	 IF NOT _done THEN 
    		CALL csdn.pro_flow_modify(v_number,v_city);
    	 END IF; 
    	 UNTIL _done=1 END REPEAT;
        CLOSE cur_all; 
        	/*展示下所有的行转列的数据**/
    	SELECT * FROM csdn.flow_tmp;      
    END$$   
    DELIMITER ;

### 3 ，行里变化存储过程 ###

通过查询系统表 information\_schema.\`COLUMNS\` 来获取测试表 flow\_table 的所有列，然后写动态 SQL ，来把列的值录入到临时表 flow\_tmp 中。

DELIMITER $$
    DROP PROCEDURE IF EXISTS csdn.`pro_flow_modify`$$
    CREATE PROCEDURE csdn.`pro_flow_modify`(p_Number INT,p_city VARCHAR(10))
    BEGIN
    	DECLARE v_column_name VARCHAR(10) DEFAULT '';
    	DECLARE v_exe_sql VARCHAR(1000) DEFAULT '';
    	DECLARE v_start_wm VARCHAR(10) DEFAULT '';
    	DECLARE v_end_wm VARCHAR(10) DEFAULT '';
    	DECLARE v_num  DECIMAL(10,2) DEFAULT 0;
    	
    	DECLARE i INT DEFAULT 1;
    	DECLARE v_Number INT DEFAULT 0;
    	SET v_Number=p_Number;
    	
    	DELETE FROM csdn.flow_n_columns;
    	DELETE FROM csdn.flow_tmp WHERE Number=v_Number;
    	
    	
    	/*把测试表flow_table的所有字段都录入字段临时表中，这样就达到了从列变成行的目的*/
    	INSERT INTO flow_n_columns
    	SELECT t.`COLUMN_NAME` FROM information_schema.`COLUMNS` t WHERE t.`TABLE_NAME`='flow_table' AND t.`TABLE_SCHEMA`='csdn' AND t.`COLUMN_NAME` NOT IN('ID','Number','City');
    	SELECT column_name INTO v_column_name FROM csdn.flow_n_columns LIMIT 1;
    	
    	/*开始循环遍历字段临时表的字段数据，并且把字段值放入临时表flow_tmp里面*/
    	WHILE i>0 DO
    		SET v_exe_sql=CONCAT('INSERT INTO csdn.flow_tmp(Number,City,wm_str,Wm) select ',v_Number,',\'',p_city, '\',\'',v_column_name,'\',',v_column_name,' from csdn.flow_table WHERE flow_table.Number=',v_Number,';');
    		SET @sql=v_exe_sql;
    		PREPARE s1 FROM @sql;
    		EXECUTE s1;
    		DEALLOCATE PREPARE s1; 
    		DELETE FROM csdn.flow_n_columns WHERE column_name=v_column_name;
    		SELECT column_name INTO v_column_name FROM csdn.flow_n_columns LIMIT 1;
    		SELECT COUNT(1) INTO i FROM csdn.flow_n_columns ;
    		DELETE FROM csdn.flow_tmp WHERE Wm=0;
    	END WHILE;
    
    	/*由于触发器是不支持动态sql，所以不能使用while循环，动态遍历所有统计列的，只能写死列了，如下所示：
    	现在一个个insert只能写死了, flow_table表有多少个统计列就写多少个insert sql，以后新添加一个列，就在这里新添加一条insertsql语句
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201403',wm201403 FROM flow_table WHERE Number=v_Number ;
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201404',wm201404 FROM flow_table WHERE Number=v_Number ;
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201405',wm201405 FROM flow_table WHERE Number=v_Number ;
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201406',wm201406 FROM flow_table WHERE Number=v_Number ;
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201407',wm201407 FROM flow_table WHERE Number=v_Number ;
    	INSERT INTO flow_tmp(Number,City,wm_str,Wm) SELECT v_Number,p_city,'wm201408',wm201408 FROM flow_table WHERE Number=v_Number ;
    	*/
    	
    	/*清除掉不数据=0的列*/
    	DELETE FROM csdn.flow_tmp WHERE Wm=0 OR Wm IS NULL;
    	
    	SELECT wm_str INTO v_start_wm FROM csdn.flow_tmp WHERE Number=v_Number ORDER BY wm_str ASC LIMIT 1;
    	SELECT wm_str INTO v_end_wm FROM csdn.flow_tmp WHERE Number=v_Number ORDER BY wm_str DESC LIMIT 1;
    	SELECT SUM(Wm) INTO v_num FROM csdn.flow_tmp WHERE Number=v_Number;	
    	
    
        END$$
    
    DELIMITER ;

### 4 ，列变行结果展示 ###

临时表的所有数据：

mysql> SELECT * FROM csdn.flow_tmp;
    +--------+----------+----------+--------+
    | Number | City     | wm_str   | Wm     |
    +--------+----------+----------+--------+
    |      1 | shanghai | wm201403 | 100.20 |
    |      1 | shanghai | wm201404 | 180.40 |
    |      1 | shanghai | wm201405 | 141.00 |
    |      1 | shanghai | wm201406 | 164.00 |
    |      1 | shanghai | wm201407 | 124.00 |
    |      1 | shanghai | wm201408 | 127.00 |
    |      2 | shanghai | wm201403 | 110.23 |
    |      2 | shanghai | wm201404 | 180.34 |
    |      2 | shanghai | wm201405 | 141.23 |
    |      2 | shanghai | wm201406 | 104.78 |
    |      2 | shanghai | wm201407 | 124.67 |
    |      2 | shanghai | wm201408 | 127.45 |
    |      3 | beijing  | wm201403 | 123.23 |
    |      3 | beijing  | wm201404 | 110.34 |
    |      3 | beijing  | wm201405 | 131.33 |
    |      3 | beijing  | wm201406 | 154.58 |
    |      3 | beijing  | wm201407 | 154.67 |
    |      3 | beijing  | wm201408 | 167.45 |
    |      4 | hangzhou | wm201404 | 110.34 |
    |      4 | hangzhou | wm201405 | 131.33 |
    |      4 | hangzhou | wm201406 | 154.58 |
    |      4 | hangzhou | wm201407 | 154.67 |
    |      5 | hangzhou | wm201405 | 131.33 |
    |      5 | hangzhou | wm201406 | 154.58 |
    |      5 | hangzhou | wm201407 | 154.67 |
    +--------+----------+----------+--------+
    25 rows in set (0.00 sec)
    mysql>

统计每个用户的使用总量为：

mysql> SELECT Number,SUM(Wm) 'total_num' FROM flow_tmp GROUP BY Number ORDER BY Number;
    +--------+-----------+
    | Number | total_num | +--------+-----------+ |      1 | 836.60 |
    | 2 |    788.70 | |      3 | 841.60 |
    | 4 |    550.92 | |      5 | 440.58 |
    +--------+-----------+
    5 rows in set (0.00 sec)
    
    mysql>

## 二，行变列例子演示 ##

### 1 ，准备测试数据 ###

USE csdn;
    DROP TABLE IF EXISTS csdn.tb;
    CREATE TABLE tb(`cname` VARCHAR(10),cource VARCHAR(10),score INT) ENGINE=INNODB;
    
    INSERT INTO tb VALUES('张三','语文',74);
    INSERT INTO tb VALUES('张三','数学',83);
    INSERT INTO tb VALUES('张三','物理',93);
    INSERT INTO tb VALUES('李四','语文',74);
    INSERT INTO tb VALUES('李四','数学',84);
    INSERT INTO tb VALUES('李四','物理',94);
    
    SELECT * FROM tb;

需要得到的结果是：

\+--------------------+--------+--------+--------+-----------+--------------+

| 姓名               | 语文   | 数学   | 物理   | 总成绩    | 平均成绩     |

\+--------------------+--------+--------+--------+-----------+--------------+

| 张三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

| 李四               |  74.00 |  84.00 |  94.00 |    252.00 |        84.00 |

| 总成绩平均数       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

\+--------------------+--------+--------+--------+-----------+--------------+

2 ，利用 SUM(IF())  生成列  + WITH ROLLUP  生成汇总行 , 并利用  IFNULL 将汇总行标题显示为  Total\_num

SQL 代码块如下：

SELECT cname AS "姓名",
    	SUM(IF(cource="语文",score,0)) AS "语文",
    	SUM(IF(cource="数学",score,0)) AS "数学",
    	SUM(IF(cource="物理",score,0)) AS "物理",
    	SUM(score) AS "总成绩",
    	ROUND(AVG(score),2) AS "平均成绩"
    FROM tb 
    GROUP BY cname
    UNION ALL
    SELECT
    	"总成绩平均数",
    	ROUND(AVG(`语文`),2) , ROUND(AVG(`数学`),2), ROUND(AVG(`物理`),2), ROUND(AVG(`总成绩`),2), ROUND(AVG(`平均成绩`),2)
    FROM(
    	SELECT "all",cname AS "姓名",
    		SUM(IF(cource="语文",score,0)) AS "语文",
    		SUM(IF(cource="数学",score,0)) AS "数学",
    		SUM(IF(cource="物理",score,0)) AS "物理",
    		SUM(score) AS "总成绩",
    		AVG(score) AS "平均成绩"
    	FROM tb 
    	GROUP BY cname
    )tb2 
    GROUP BY tb2.all;

执行结果正确，如下所示：

\+--------------------+--------+--------+--------+-----------+--------------+

| 姓名               | 语文   | 数学   | 物理   | 总成绩    | 平均成绩     |

\+--------------------+--------+--------+--------+-----------+--------------+

| 张三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

| 李四               |  74.00 |  84.00 |  94.00 |    252.00 |        84.00 |

| 总成绩平均数       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

\+--------------------+--------+--------+--------+-----------+--------------+

### 3 ，利用 max(CASE ... WHEN ... THEN .. ELSE END) AS " 语文 " 的方式来实现 ###

SQL代码如下：

SELECT 
    	cname AS "姓名",
    	MAX(CASE cource WHEN "语文" THEN score ELSE 0 END) AS "语文", 
    	MAX(CASE cource WHEN "数学" THEN score ELSE 0 END) AS "数学", 
    	MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理", 
    	SUM(score) AS "总成绩",
    	ROUND(AVG(score) ,2) AS "平均成绩"
    FROM tb 
    GROUP BY `cname`
    UNION ALL
    SELECT
    	"总成绩平均数",
    	ROUND(AVG(`语文`),2) , ROUND(AVG(`数学`),2), ROUND(AVG(`物理`),2), ROUND(AVG(`总成绩`),2), ROUND(AVG(`平均成绩`),2)
    FROM(	SELECT 'all' ,  
    		cname AS "姓名",
    		MAX(CASE cource WHEN "语文" THEN score ELSE 0 END) AS "语文", 
    		MAX(CASE cource WHEN "数学" THEN score ELSE 0 END) AS "数学", 
    		MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理", 
    		SUM(score) AS "总成绩",
    		ROUND(AVG(score) ,2) AS "平均成绩"
    	FROM tb 
    	GROUP BY `cname` 
    )tb2 GROUP BY tb2.all

执行结果正确，如下所示：

\+--------------------+--------+--------+--------+-----------+--------------+

| 姓名               | 语文   | 数学   | 物理   | 总成绩    | 平均成绩     |

\+--------------------+--------+--------+--------+-----------+--------------+

| 张三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

| 李四               |  74.00 |  84.00 |  94.00 |    252.00 |        84.00 |

| 总成绩平均数       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

\+--------------------+--------+--------+--------+-----------+--------------+

### 4 ，利用  WITH rollup 结果不符合 ###

SQL代码如下：

SELECT IFNULL(cname,'总平均数') AS "姓名",
    	MAX(CASE cource WHEN "语文" THEN score ELSE 0 END) AS "语文", 
    	MAX(CASE cource WHEN "数学" THEN score ELSE 0 END) AS "数学", 
    	MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理", 
    	ROUND(AVG(score),2) AS "总成绩",
    	ROUND(AVG(avg_score),2) AS "平均成绩" 
    	FROM(
    	SELECT   
    		cname ,
    		IFNULL(cource,'total') cource,
    		SUM(score) AS score,
    		ROUND(AVG(score) ,2) AS avg_score
    	FROM tb 
    	GROUP BY `cname`,cource WITH ROLLUP HAVING cname IS NOT NULL
    	)tb2 
    	GROUP BY  tb2.cname WITH ROLLUP;

执行结果不对，总平均数栏目，里面各科比较语文数学的班级平均数不对，如下所示：

mysql>	 SELECT IFNULL(cname,'总平均数') AS "姓名",
    	-> MAX(CASE cource WHEN "语文" THEN score ELSE 0 END) AS "语文", 
    	-> MAX(CASE cource WHEN "数学" THEN score ELSE 0 END) AS "数学", 
    	-> MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理", 
    	-> ROUND(AVG(score),2) AS "总成绩",
    	-> ROUND(AVG(avg_score),2) AS "平均成绩" 
    	->	 FROM(
    	-> SELECT   
    	-> 
    Display ALL 793 possibilities? (Y OR n) 
    	-> cname ,
    	-> 
    Display ALL 793 possibilities? (Y OR n) 
    	-> IFNULL(cource,'total') cource,
    	-> 
    Display ALL 793 possibilities? (Y OR n) 
    	-> SUM(score) AS score,
    	-> 
    Display ALL 793 possibilities? (Y OR n) 
    	-> ROUND(AVG(score) ,2) AS avg_score
    	-> FROM tb 
    	-> GROUP BY `cname`,cource WITH ROLLUP HAVING cname IS NOT NULL
    	-> )tb2 
    	-> GROUP BY  tb2.cname WITH ROLLUP;
    +--------------+--------+--------+--------+-----------+--------------+
    | 姓名		 | 语文   | 数学   | 物理   | 总成绩	| 平均成绩	 |
    +--------------+--------+--------+--------+-----------+--------------+
    | 张三		 |	 74 |	 83 |	 93 |	125.00 |		83.33 |
    | 李四		 |	 74 |	 84 |	 94 |	126.00 |		84.00 |
    | 总平均数	 |	 74 |	 84 |	 94 |	125.50 |		83.67 |
    +--------------+--------+--------+--------+-----------+--------------+
    3 ROWS IN SET, 1 warning (0.00 sec)
    
    mysql>

总结： WITH rollup中对求列的总数是OK的，但是求列的平均数有偏差，这里场景使用不是恰当。

### 5 ，使用动态 SQL 来实现 ###

SQL 代码块如下：

/*仅仅班级成员部分*/
    SET @a=''; 
    SELECT @a:=CONCAT(@a,'SUM(IF(cource=\'',cource,'\'',',score,0)) AS ',cource,',') FROM (SELECT DISTINCT cource FROM tb) A;
    SET @a=CONCAT(@a,"ROUND(AVG(score) ,2) AS \"平均成绩\"");
    SET @b=CONCAT('SELECT IFNULL(cname,\'总成绩\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"总成绩\" FROM tb GROUP BY cname ');
    
    /*班级成员总计部分**/
    SET @a2="";
    SET @b2=CONCAT('SELECT "all",IFNULL(cname,\'总成绩\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"总成绩\" FROM tb GROUP BY cname ');
    SELECT @a2:=CONCAT(@a2,'ROUND(AVG(`',cource,'`),2),') FROM (SELECT DISTINCT cource FROM tb) A;
    SET @a2=CONCAT(@a2," ROUND(AVG(`平均成绩`),2),ROUND(AVG(`总成绩`),2) ");
    SET @c=CONCAT("SELECT \"班级平均数\",",LEFT(@a2,LENGTH(@a)-1)," FROM(",@b2,")tb2 GROUP BY tb2.all;");
    SET @d=CONCAT(@b," UNION ALL ",@c);
    
    PREPARE stmt1 FROM @d;
    EXECUTE stmt1;

查看执行结果如下，已经达到效果：

mysql> /*仅仅班级成员部分*/
    mysql> SET @a=''; 
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SELECT @a:=CONCAT(@a,'SUM(IF(cource=\'',cource,'\'',',score,0)) AS ',cource,',') FROM (SELECT DISTINCT cource FROM tb) A;
    +-----------------------------------------------------------------------------------------------------------------------------------+
    | @a:=CONCAT(@a,'SUM(IF(cource=\'',cource,'\'',',score,0)) AS ',cource,',') |
    +-----------------------------------------------------------------------------------------------------------------------------------+
    | SUM(IF(cource='语文',score,0)) AS 语文, |
    | SUM(IF(cource='语文',score,0)) AS 语文,SUM(IF(cource='数学',score,0)) AS 数学, |
    | SUM(IF(cource='语文',score,0)) AS 语文,SUM(IF(cource='数学',score,0)) AS 数学,SUM(IF(cource='物理',score,0)) AS 物理, |
    +-----------------------------------------------------------------------------------------------------------------------------------+
    3 ROWS IN SET (0.00 sec)
    
    mysql> SET @a=CONCAT(@a,"ROUND(AVG(score) ,2) AS \"平均成绩\"");
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SET @b=CONCAT('SELECT IFNULL(cname,\'总成绩\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"总成绩\" FROM tb GROUP BY cname ');
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> 
    mysql> /*班级成员总计部分**/
    mysql> SET @a2="";
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SET @b2=CONCAT('SELECT "all",IFNULL(cname,\'总成绩\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"总成绩\" FROM tb GROUP BY cname ');
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SELECT @a2:=CONCAT(@a2,'ROUND(AVG(`',cource,'`),2),') FROM (SELECT DISTINCT cource FROM tb) A;
    +-----------------------------------------------------------------------+
    | @a2:=CONCAT(@a2,'ROUND(AVG(`',cource,'`),2),') |
    +-----------------------------------------------------------------------+
    | ROUND(AVG(`语文`),2), |
    | ROUND(AVG(`语文`),2),ROUND(AVG(`数学`),2), |
    | ROUND(AVG(`语文`),2),ROUND(AVG(`数学`),2),ROUND(AVG(`物理`),2), |
    +-----------------------------------------------------------------------+
    3 ROWS IN SET (0.00 sec)
    
    mysql> SET @a2=CONCAT(@a2," ROUND(AVG(`平均成绩`),2),ROUND(AVG(`总成绩`),2) ");
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SET @c=CONCAT("SELECT \"班级平均数\",",LEFT(@a2,LENGTH(@a)-1)," FROM(",@b2,")tb2 GROUP BY tb2.all;");
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> SET @d=CONCAT(@b," UNION ALL ",@c);
    QUERY OK, 0 ROWS affected (0.00 sec)
    
    mysql> 
    mysql> PREPARE stmt1 FROM @d;
    QUERY OK, 0 ROWS affected (0.00 sec)
    Statement prepared
    
    mysql> EXECUTE stmt1;
    +---------------------------+--------+--------+--------+--------------+-----------+
    | IFNULL(cname,'总成绩') | 语文   | 数学 | 物理   | 平均成绩 | 总成绩    | +---------------------------+--------+--------+--------+--------------+-----------+ | 张三                      | 74.00 |  83.00 | 93.00 |        83.33 | 250.00 |
    | 李四 |  74.00 | 84.00 |  94.00 | 84.00 |    252.00 | | 班级平均数                | 74.00 |  83.50 | 93.50 |        83.67 | 251.00 |
    +---------------------------+--------+--------+--------+--------------+-----------+
    3 ROWS IN SET (0.00 sec)
    
    mysql>