# 创建数据表 CREATE TABLE ChengJi ( Name varchar(32), Subject varchar(32), Result int(10) ); # 插入数据 insert into ChengJi values ('张三', '语文', 80), ('张三', '数学', 90), ('张三', '物理', 85), ('李四', '语文', 85), ('李四', '数学', 92), ('李四', '物理', 82);
整体分两步走
1、先预处理数据,将数据进行初步的行转列,便于后续的分组处理
select Name, case when Subject = '语文' then Result else 0 end as 'Chinese', case when Subject = '数学' then Result else 0 end as 'Math', case when Subject = '物理' then Result else 0 end as 'Pha' from ChengJi;
2、对预处理完毕的数据进行分组聚合,使多行数据汇聚到一个组内,达到数据集中的结果,这其中要注意的一点是:要明确按照哪个字段进行聚合操作。
with t1 as(select Name, case when Subject = '语文' then Result else 0 end as 'Chinese', case when Subject = '数学' then Result else 0 end as 'Math', case when Subject = '物理' then Result else 0 end as 'Pha' from ChengJi) select Name, sum(Chinese) as 'Chinese', sum(Math) as 'Math', sum(Pha) as 'Pha' from t1 group by Name;
为便于理解,我们将刚才已经转置好的结果插入到一个结果表内
1、创建一个结果表
create table ChengJi_2( Name varchar(255), Chinese int, Math int, Pha int );
2、将行转列结果插入到结果表
insert into chengji_2 with t1 as(select Name, case when Subject = '语文' then Result else 0 end as 'Chinese', case when Subject = '数学' then Result else 0 end as 'Math', case when Subject = '物理' then Result else 0 end as 'Pha' from ChengJi) select Name, sum(Chinese) as 'Chinese', sum(Math) as 'Math', sum(Pha) as 'Pha' from t1 group by Name ;
3、对结果表进行列转行的操作,列转行相对于行转列较为简单,可直接使用 union all 进行操作。
select Name,Chinese from ChengJi_2 union all select Name,Math from ChengJi_2 union all select Name,Pha from ChengJi_2;
但是对于一些特殊的行列转置,以上方法就不再使用,通常情况下,我们的行列转置是有可以进行分组聚合操作可以完成的,而生产实践中也多数如此,但是有时有一些特殊的操作是以上方法无法完成的,这就需要一些特殊的行列转置来完成,对此,我给出了以下的方案。
1、准备工作,创建数据表并插入数据
CREATE TABLE 2003a ( seat varchar(255) , status varchar(255) , rowid varchar(255) ) ; INSERT INTO 2003a VALUES ('2', '已预订', 'A'); INSERT INTO 2003a VALUES ('3', '未预订', 'A'); INSERT INTO 2003a VALUES ('4', '未预订', 'A'); INSERT INTO 2003a VALUES ('5', '未预订', 'A'); INSERT INTO 2003a VALUES ('6', '未预订', 'B'); INSERT INTO 2003a VALUES ('7', '未预订', 'B'); INSERT INTO 2003a VALUES ('8', '未预订', 'B'); INSERT INTO 2003a VALUES ('9', '未预订', 'B'); INSERT INTO 2003a VALUES ('10', '未预订', 'B'); INSERT INTO 2003a VALUES ('11', '未预订', 'C'); INSERT INTO 2003a VALUES ('12', '已预订', 'C'); INSERT INTO 2003a VALUES ('13', '已预订', 'C'); INSERT INTO 2003a VALUES ('14', '未预订', 'C'); INSERT INTO 2003a VALUES ('15', '未预订', 'C'); INSERT INTO 2003a VALUES ('16', '未预订', 'D'); INSERT INTO 2003a VALUES ('17', '未预订', 'D'); INSERT INTO 2003a VALUES ('18', '未预订', 'D'); INSERT INTO 2003a VALUES ('19', '未预订', 'D'); INSERT INTO 2003a VALUES ('20', '已预订', 'D');
2、明确需求
原有表的结构:
2,已预订,A 3,未预订,A
需要完成的工作:
2,3 已预定,未预定 A,A
在这里我们可以很明显的看出,我们需要做的就是如何进行 行转列/列转行 的操作,在这里的行列转置是整行/整列进行转置,不再是依靠某个字段进行分组处理或者使用 union all 进行整体操作,因此,我是用以下方案来完成。
1、对原表字段进行 group_concat,指定 “,”为字段值之间的分隔符
SELECT GROUP_CONCAT(rowid ORDER BY rowid ASC SEPARATOR ', ') AS rowid, GROUP_CONCAT(status ORDER BY rowid ASC SEPARATOR ', ') AS status, GROUP_CONCAT(seat ORDER BY rowid ASC SEPARATOR ', ') AS seat FROM ( SELECT rowid, status, seat from `2003a` ) AS subquery
2、将所有的字段按照值聚合到一个数据表格内之后,我们可以使用 union all 来进行字段拆分
with t1 as (SELECT GROUP_CONCAT(rowid ORDER BY rowid ASC SEPARATOR ', ') AS rowid, GROUP_CONCAT(status ORDER BY rowid ASC SEPARATOR ', ') AS status, GROUP_CONCAT(seat ORDER BY rowid ASC SEPARATOR ', ') AS seat FROM ( SELECT rowid, status, seat from `2003a` ) AS subquery) select seat from t1 union all select status from t1 union all select rowid from t1
3、使用 SUBSTRING_INDEX来进行拆分,将所有的字段值拆分成单独的值
with t1 as (SELECT GROUP_CONCAT(rowid ORDER BY rowid ASC SEPARATOR ', ') AS rowid, GROUP_CONCAT(status ORDER BY rowid ASC SEPARATOR ', ') AS status, GROUP_CONCAT(seat ORDER BY rowid ASC SEPARATOR ', ') AS seat FROM ( SELECT rowid, status, seat from `2003a` ) AS subquery) ,t2 as (select seat from t1 union all select status from t1 union all select rowid from t1) select SUBSTRING_INDEX(seat,',',1) as p1, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',2),',',-1) as p2, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',3),',',-1) as p3, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',4),',',-1) as p4, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',5),',',-1) as p5, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',6),',',-1) as p6, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',7),',',-1) as p7, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',8),',',-1) as p8, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',9),',',-1) as p9, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',10),',',-1) as p10, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',11),',',-1) as p11, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',12),',',-1) as p12, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',13),',',-1) as p13, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',14),',',-1) as p14, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',15),',',-1) as p15, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',16),',',-1) as p16, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',17),',',-1) as p17, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',18),',',-1) as p18, SUBSTRING_INDEX(SUBSTRING_INDEX(seat,',',19),',',-1) as p19 from t2
在这里需要注意的是:第一个SUBSTRING_INDEX我们取的是源数据的第一个值,第二个SUBSTRING_INDEX以及之后的,我们取得是源数据的倒数第一个值,因此这里需要注意一下我们给到的是“-1”
至此,我们使用group_concat()以及SUBSTRING_INDEX()来达到了特殊的行列转置操作。
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