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今天被问到列转行的问题，竟然没有回答上来，回想自己也是数据开发人员，平时的积累真是不到位，下面总结一下列转行。
假设咱们有一个学生得分数据表：student_score
CREATE TABLE student_scores ( user_name character varying(30) NOT NULL, -- 学生名称 subject character varying(30) NOT NULL, -- 课程名称 score integer, -- 得分 CONSTRAINT student_scores_pkey PRIMARY KEY (user_name, subject) ); COMMENT ON COLUMN student_scores.user_name IS ‘学生名称‘; COMMENT ON COLUMN student_scores.subject IS ‘课程名称‘; COMMENT ON COLUMN student_scores.score IS ‘得分‘;
是postgresql的语法，就四个字段，下面是数据库内容：
那么我希望把这些数据用另外的一种方式展现，比如：
那么如何使用sql实现哪？下面我贴出来代码：
第一种办法，逻辑简单 左关联：
SELECT a.user_name, b.score as "语文", c.score as "数学", d.score as "英语", e.score as "生物" FROM (select distinct user_name from student_scores) a left join (select score, user_name FROM student_scores where subject = ‘语文‘) b on b.user_name=a.user_name left join (select score, user_name FROM student_scores where subject = ‘数学‘) c on c.user_name=a.user_name left join (select score, user_name FROM student_scores where subject = ‘英语‘) d on d.user_name=a.user_name left join (select score, user_name FROM student_scores where subject = ‘生物‘) e on e.user_name=a.user_name
第二种方法，必然好了一些：
SELECT user_name, MAX(CASE subject WHEN ‘语文‘ THEN Score ELSE 0 END) AS "语文", MAX(CASE subject WHEN ‘数学‘ THEN Score ELSE 0 END) AS "数学", MAX(CASE subject WHEN ‘英语‘ THEN Score ELSE 0 END) AS "英语", MAX(CASE subject WHEN ‘生物‘ THEN Score ELSE 0 END) AS "生物" FROM student_scores GROUP BY user_name
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原文地址：http://www.cnblogs.com/liqiu/p/4925515.html
