[置顶] sql行转列

行转列 

在sqlserver 数据库中提供 PIVOT用于将列值旋转为列名（即行转列），在SQL Server 2000可以用聚合函数配合CASE语句实现

PIVOT的一般语法是：PIVOT(聚合函数(列) FOR 列 in (…) )AS P

完整语法：

table_source

PIVOT(

聚合函数（value_column）

FOR pivot_column

IN(<column_list>)

)

 

UNPIVOT用于将列明转为列值（即列转行），在SQL Server 2000可以用UNION来实现

完整语法：

table_source

UNPIVOT(

value_column

FOR pivot_column

IN(<column_list>)

)

由于项目使用的是mysql数据库，不提供 PIVOT函数，总结下mysql下实现行转列的集中方法

创建表

CREATE TABLE `t_score` (
  `id` int(32) NOT NULL,
  `name` varchar(10) NOT NULL,
  `course` varchar(10) DEFAULT NULL,
  `score` int(10) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `t_score`
-- ----------------------------
BEGIN;
INSERT INTO `t_score` VALUES ('1', '张三', '语文', '80'), ('2', '张三', '数学', '85'), ('3', '张三', '英语', '90'), ('4', '李四', '语文', '88'), ('5', '李四', '数学', '91'), ('6', '李四', '英语', '79');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

法一：

SELECT DISTINCT a.name,
(SELECT score FROM t_score b WHERE a.name=b.name AND b.course='语文')AS'语文',
(SELECT score FROM t_score b WHERE a.name=b.name AND b.course='数学')AS'数学',
(SELECT score FROM t_score b WHERE a.name=b.name AND b.course='英语')AS'英语'
FROM t_score a

法二：

SELECT name,
SUM(IF (course = '语文' , score , null ) ) as '语文',
SUM(IF (course = '数学' , score , null ) ) as '数学',
SUM(IF (course = '英语' , score , null ) ) as '英语 '
FROM t_score GROUP BY name

或

SELECT name,
SUM(IF (course = '语文' , score , null ) ) as '语文',
SUM(IF (course = '数学' , score , null ) ) as '数学',
SUM(IF (course = '英语' , score , null ) ) as '英语 '
FROM t_score GROUP BY name

法三：

存储过程：

mysql版

BEGIN
#课程名称
DECLARE course_n VARCHAR(20);
#所有课程数量
DECLARE count INT;
#计数器
DECLARE i INT DEFAULT 0;
#拼接SQL字符串
SET @s = 'SELECT name';
SET count = (SELECT  COUNT(distinct course) FROM t_score);
WHILE i < count DO
SET course_n = (SELECT course FROM t_score LIMIT i,1);
SET @s = CONCAT(@s, ', SUM(CASE  course WHEN  ','\'', course_n,'\'',' THEN score END )',' AS ','\'',course_n,'\'');
SET i = i+1;
END WHILE;
SET @s = CONCAT(@s, ' FROM t_score GROUP BY name');
#用于调试
#SELECT @s;
PREPARE stmt FROM @s;
EXECUTE stmt;
END