mysql行轉列列轉行在線求助！！！！！！！！！！

mysql 行轉列、列轉行求助！！！！！

現在需求是將表t1轉化爲表t2，要求僅查詢一次t1表。  附1是表ddl語句，附2是使用union all寫的SQL，由於多次查詢表t1，所以當t1中指標很多（例如h_score、w_score、x_score....）的情況下不適用,尋求最優解。

表t1如圖所示：

    

                                                           表t1

                                                             表t2

 

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附1

DROP TABLE IF EXISTS `t1`;
CREATE TABLE `t1` (
  `user_name` varchar(30) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `course` varchar(30) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `h_score` int(10) DEFAULT NULL,
  `w_score` int(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


BEGIN;
INSERT INTO `t1` VALUES ('張三', '英語', 50, 60);
INSERT INTO `t1` VALUES ('張三', '俄語', 70, 80);
INSERT INTO `t1` VALUES ('張三', '日語', 80, 90);
INSERT INTO `t1` VALUES ('李四', '英語', 45, 55);
INSERT INTO `t1` VALUES ('李四', '俄語', 65, 75);
INSERT INTO `t1` VALUES ('李四', '日語', 85, 95);
COMMIT;

附2

select user_name, 
'h_score' as d,
sum(case when course = '英語' then h_score else 0 end) as '英語',
sum(case when course = '俄語' then h_score else 0 end) as '俄語',
sum(case when course = '日語' then h_score else 0 end) as '日語'
from t1
GROUP BY user_name
union all 
select user_name, 
'wscore' as d,
sum(case when course = '英語' then w_score else 0 end) as '英語',
sum(case when course = '俄語' then w_score else 0 end) as '俄語',
sum(case when course = '日語' then w_score else 0 end) as '日語'
from t1
GROUP BY user_name