前言：

mysql行列變化，最難的就是將多個列變成多行，使用的比較多的是統計學中行變列，列變行，沒有找到現成的函式或者語句，所以自己寫了儲存過程，使用動態sql來實現，應用業務場景，使用者每個月都有使用記錄數錄入一張表，一個月一個欄位，所以表的欄位是動態增長的，現在需要實時統計當前使用者使用的總數量，如果你知道有多少個欄位，那麼可以用select c1+c2+c3+…. From tbname where tid=’111’;來實現，但是關鍵是這個都是動態的，所以在應用程式端來實現確實不適宜，可以放在資料庫後臺在儲存過程裡實現。

而且在行變成列中，如果要寫單個sql來實現，列的數目就需要寫死，因為如果不知道要展示成多少列的話，就需要用動態變數，而一條

一，列變成行例子演示

1，準備測試資料

這是基礎資料表，裡面有多個欄位wm201403……，現在需要把N個這樣的列變成行資料。

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;

錄入一批測試資料：

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;

需要達到的統計效果是：

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

| 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，儲存過程遍歷：

這個儲存過程建立了2張臨時表，查詢測試表資料形成遊標，遍歷遊標根據主鍵Number來呼叫pro_flow_modify儲存過程進行行列變化。程式碼如下：

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;         /*定義遊標*/    DECLARE cur_all CURSOR FOR SELECT Number,City FROM csdn.`flow_table`;    /**這裡如果需要定義下當NOT FOUND的時候，EXIT退出遊標遍歷，不然如果設定成CONTINUE會一直執行下去。*/    DECLARE EXIT HANDLER FOR NOT FOUND BEGIN SET _done=1;END;                 /*建立臨時表，存放所有欄位的臨時表*/ DROP TABLE IF EXISTS flow_n_columns; CREATE TABLE `flow_n_columns` (   `column_name` VARCHAR(10) NOT NULL ) ENGINE=INNODB DEFAULT CHARSET=utf8; /*存放最終變成行的資料表*/ 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;      /*展示下所有的行轉列的資料**/ SELECT * FROM csdn.flow_tmp;      END$$   DELIMITER ;

3，行裡變化儲存過程

通過查詢系統表information_schema.`COLUMNS`來獲取測試表flow_table的所有列，然後寫動態SQL，來把列的值錄入到臨時表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;   /*把測試表flow_table的所有欄位都錄入欄位臨時表中，這樣就達到了從列變成行的目的*/ 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;  /*開始迴圈遍歷欄位臨時表的欄位資料，並且把欄位值放入臨時表flow_tmp裡面*/ 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; /*由於觸發器是不支援動態sql，所以不能使用while迴圈，動態遍歷所有統計列的，只能寫死列了，如下所示： 現在一個個insert只能寫死了, flow_table表有多少個統計列就寫多少個insert sql，以後新新增一個列，就在這裡新新增一條insertsql語句 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 ; */  /*清除掉不資料=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，列變行結果展示

臨時表的所有資料：

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>

統計每個使用者的使用總量為：

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，行變列例子演示

1，準備測試資料

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('張三','語文',74);INSERT INTO tb VALUES('張三','數學',83);INSERT INTO tb VALUES('張三','物理',93);INSERT INTO tb VALUES('李四','語文',74);INSERT INTO tb VALUES('李四','數學',84);INSERT INTO tb VALUES('李四','物理',94);SELECT * FROM tb;

需要得到的結果是：

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

| 姓名               | 語文   | 數學   | 物理   | 總成績    | 平均成績     |

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

| 張三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

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

| 總成績平均數       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

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

2，利用SUM(IF()) 生成列 + WITH ROLLUP 生成彙總行,並利用 IFNULL將彙總行標題顯示為 Total_num

SQL程式碼塊如下：

SELECT cname AS "姓名", SUM(IF(cource="語文",score,0)) AS "語文", SUM(IF(cource="數學",score,0)) AS "數學", SUM(IF(cource="物理",score,0)) AS "物理", SUM(score) AS "總成績", ROUND(AVG(score),2) AS "平均成績"FROM tb GROUP BY cnameUNION ALLSELECT "總成績平均數", ROUND(AVG(`語文`),2) , ROUND(AVG(`數學`),2), ROUND(AVG(`物理`),2), ROUND(AVG(`總成績`),2), ROUND(AVG(`平均成績`),2)FROM( SELECT "all",cname AS "姓名",  SUM(IF(cource="語文",score,0)) AS "語文",  SUM(IF(cource="數學",score,0)) AS "數學",  SUM(IF(cource="物理",score,0)) AS "物理",  SUM(score) AS "總成績",  AVG(score) AS "平均成績" FROM tb  GROUP BY cname)tb2 GROUP BY tb2.all;

執行結果正確，如下所示：

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

| 姓名               | 語文   | 數學   | 物理   | 總成績    | 平均成績     |

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

| 張三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

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

| 總成績平均數       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

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

3，利用max(CASE ... WHEN ... THEN .. ELSE END) AS "語文"的方式來實現

 SQL程式碼如下：

SELECT  cname AS "姓名", MAX(CASE cource WHEN "語文" THEN score ELSE 0 END) AS "語文",  MAX(CASE cource WHEN "數學" THEN score ELSE 0 END) AS "數學",  MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理",  SUM(score) AS "總成績", ROUND(AVG(score) ,2) AS "平均成績"FROM tb GROUP BY `cname`UNION ALLSELECT "總成績平均數", ROUND(AVG(`語文`),2) , ROUND(AVG(`數學`),2), ROUND(AVG(`物理`),2), ROUND(AVG(`總成績`),2), ROUND(AVG(`平均成績`),2)FROM( SELECT 'all' ,    cname AS "姓名",  MAX(CASE cource WHEN "語文" THEN score ELSE 0 END) AS "語文",   MAX(CASE cource WHEN "數學" THEN score ELSE 0 END) AS "數學",   MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理",   SUM(score) AS "總成績",  ROUND(AVG(score) ,2) AS "平均成績" FROM tb  GROUP BY `cname` )tb2 GROUP BY tb2.all

執行結果正確，如下所示：

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

| 姓名               | 語文   | 數學   | 物理   | 總成績    | 平均成績     |

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

| 張三               |  74.00 |  83.00 |  93.00 |    250.00 |        83.33 |

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

| 總成績平均數       |  74.00 |  83.50 |  93.50 |    251.00 |        83.67 |

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

4，利用 WITH rollup結果不符合

  SELECT IFNULL(cname,'總平均數') AS "姓名", MAX(CASE cource WHEN "語文" THEN score ELSE 0 END) AS "語文",  MAX(CASE cource WHEN "數學" THEN score ELSE 0 END) AS "數學",  MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理",  ROUND(AVG(score),2) AS "總成績", ROUND(AVG(avg_score),2) AS "平均成績"     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;

執行結果不對，總平均數欄目，裡面各科比較語文數學的班級平均數不對，如下所示：

mysql>     SELECT IFNULL(cname,'總平均數') AS "姓名",    -> MAX(CASE cource WHEN "語文" THEN score ELSE 0 END) AS "語文",     -> MAX(CASE cource WHEN "數學" THEN score ELSE 0 END) AS "數學",     -> MAX(CASE cource WHEN "物理" THEN score ELSE 0 END) AS "物理",     -> ROUND(AVG(score),2) AS "總成績",    -> ROUND(AVG(avg_score),2) AS "平均成績"     ->     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         | 語文   | 數學   | 物理   | 總成績    | 平均成績     |+--------------+--------+--------+--------+-----------+--------------+| 張三         |     74 |     83 |     93 |    125.00 |        83.33 || 李四         |     74 |     84 |     94 |    126.00 |        84.00 || 總平均數     |     74 |     84 |     94 |    125.50 |        83.67 |+--------------+--------+--------+--------+-----------+--------------+3 ROWS IN SET, 1 warning (0.00 sec)mysql> 

總結： WITH rollup中對求列的總數是OK的，但是求列的平均數有偏差，這裡場景使用不是恰當。

5，使用動態SQL來實現

SQL程式碼塊如下：

/*僅僅班級成員部分*/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 \"平均成績\"");SET @b=CONCAT('SELECT IFNULL(cname,\'總成績\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"總成績\" FROM tb GROUP BY cname ');/*班級成員總計部分**/SET @a2="";SET @b2=CONCAT('SELECT "all",IFNULL(cname,\'總成績\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"總成績\" 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(`平均成績`),2),ROUND(AVG(`總成績`),2) ");SET @c=CONCAT("SELECT \"班級平均數\",",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;

檢視執行結果如下，已經達到效果：

mysql> /*僅僅班級成員部分*/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='語文',score,0)) AS 語文,                                                                                           || SUM(IF(cource='語文',score,0)) AS 語文,SUM(IF(cource='數學',score,0)) AS 數學,                                                    || SUM(IF(cource='語文',score,0)) AS 語文,SUM(IF(cource='數學',score,0)) AS 數學,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 \"平均成績\"");QUERY OK, 0 ROWS affected (0.00 sec)mysql> SET @b=CONCAT('SELECT IFNULL(cname,\'總成績\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"總成績\" FROM tb GROUP BY cname ');QUERY OK, 0 ROWS affected (0.00 sec)mysql> mysql> /*班級成員總計部分**/mysql> SET @a2="";QUERY OK, 0 ROWS affected (0.00 sec)mysql> SET @b2=CONCAT('SELECT "all",IFNULL(cname,\'總成績\'),',LEFT(@a,LENGTH(@a)-1),' ,SUM(score) AS \"總成績\" 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(`語文`),2),                                                 || ROUND(AVG(`語文`),2),ROUND(AVG(`數學`),2),                            || ROUND(AVG(`語文`),2),ROUND(AVG(`數學`),2),ROUND(AVG(`物理`),2),       |+-----------------------------------------------------------------------+3 ROWS IN SET (0.00 sec)mysql> SET @a2=CONCAT(@a2," ROUND(AVG(`平均成績`),2),ROUND(AVG(`總成績`),2) ");QUERY OK, 0 ROWS affected (0.00 sec)mysql> SET @c=CONCAT("SELECT \"班級平均數\",",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 preparedmysql> EXECUTE stmt1;+---------------------------+--------+--------+--------+--------------+-----------+| IFNULL(cname,'總成績')    | 語文   | 數學   | 物理   | 平均成績     | 總成績    |+---------------------------+--------+--------+--------+--------------+-----------+| 張三                      |  74.00 |  83.00 |  93.00 |        83.33 |    250.00 || 李四                      |  74.00 |  84.00 |  94.00 |        84.00 |    252.00 || 班級平均數                |  74.00 |  83.50 |  93.50 |        83.67 |    251.00 |+---------------------------+--------+--------+--------+--------------+-----------+3 ROWS IN SET (0.00 sec)mysql>