MySQL 给两次转置的结果集增加列头

ゝ一纸荒年。 2022-11-04 15:29 124阅读 0赞

备注:测试数据库版本为MySQL 8.0

### 文章目录 ###

*  一.需求
 *  二.解决方案
 *   *  2.1 分解求出it\_apps各部门及员工
     *  2.2 it\_apps与it\_research进行拼接

测试数据:

create table it_research(deptno int, ename varchar(20));
    
    insert into it_research values (100,'HOPKINS');
    insert into it_research values (100,'JONES');
    insert into it_research values (100,'TONEY');
    insert into it_research values (200,'MORALES');
    insert into it_research values (200,'P.WHITAKER');
    insert into it_research values (200,'MARCIANO');
    insert into it_research values (200,'ROBINSON');
    insert into it_research values (300,'LACY');
    insert into it_research values (300,'WRIGHT');
    insert into it_research values (300,'J.TAYLOR');
    
    
    CREATE TABLE IT_APPS (deptno int,ename varchar(20));
    
    insert into it_apps values (400,'CORRALES');
    insert into it_apps values (400,'MAYWEATHER');
    insert into it_apps values (400,'CASTILLO');
    insert into it_apps values (400,'MARQUEZ');
    insert into it_apps values (400,'MOSLEY');
    insert into it_apps values (500,'GATTI');
    insert into it_apps values (500,'CALZAGHE');
    insert into it_apps values (600,'LAMOTTA');
    insert into it_apps values (600,'HAGLER');
    insert into it_apps values (600,'HEARNS');
    insert into it_apps values (600,'FRAZIER');
    insert into it_apps values (700,'GUINN');
    insert into it_apps values (700,'JUDAH');
    insert into it_apps values (700,'MARGARITO');

# 一.需求 #

把两个结果集叠在一起，然后把他们转置为两列，另外，还要为每列加一个"标题"。  
例如，有两个表，它们包含公司中有关员工的信息，这些员工在不同地区从事开发工作(也即研究和应用):

mysql> select \* from it\_research;  
±-------±-----------+  
| deptno | ename |  
±-------±-----------+  
| 100 | HOPKINS |  
| 100 | JONES |  
| 100 | TONEY |  
| 200 | MORALES |  
| 200 | P.WHITAKER |  
| 200 | MARCIANO |  
| 200 | ROBINSON |  
| 300 | LACY |  
| 300 | WRIGHT |  
| 300 | J.TAYLOR |  
±-------±-----------+  
10 rows in set (0.00 sec)

mysql> select \* from it\_apps;  
±-------±-----------+  
| deptno | ename |  
±-------±-----------+  
| 400 | CORRALES |  
| 400 | MAYWEATHER |  
| 400 | CASTILLO |  
| 400 | MARQUEZ |  
| 400 | MOSLEY |  
| 500 | GATTI |  
| 500 | CALZAGHE |  
| 600 | LAMOTTA |  
| 600 | HAGLER |  
| 600 | HEARNS |  
| 600 | FRAZIER |  
| 700 | GUINN |  
| 700 | JUDAH |  
| 700 | MARGARITO |  
±-------±-----------+  
14 rows in set (0.00 sec)

要创建一个报表，它分两栏列出两个表中的员工。  
对于每一列，都返回deptno和ename。

最后，返回下列结果集:  
![image.png][]

# 二.解决方案 #

本解决方案只需要一个简单的堆叠及转置(合并后转置)并且再"拧"一次:deptno 一定在每个员工的ename之前。  
这里的技巧采用了笛卡尔积为每个deptno生产附加行，这样才有足够的行显示所有员工和deptno。

with tmp1 as
    (
    select deptno,
           ename,
           count(*) over (partition by deptno) cnt
    from it_apps
    order by deptno,ename 
    ),
    tmp2 as
    (
    select 1 id union select 2 
    ),
    tmp3 as
    (
    select deptno,
           ename,
           cnt,
           row_number() over w1 as 'rn'
      from tmp1,tmp2
    window w1 as (partition by deptno order by id,ename)
    ),
    tmp4 as
    (
    select 1 flag1,
           1 flag2,
           case when rn = 1 then deptno else concat(' ',ename) end it_dept
      from tmp3 
      where rn <= cnt + 1
    )
    ,
    tmp5 as
    (
    select deptno,
           ename,
           count(*) over (partition by deptno) cnt
    from it_research
    order by deptno,ename 
    ),
    tmp6 as
    (
    select deptno,
           ename,
           cnt,
           row_number() over w2 as 'rn'
      from tmp5,tmp2
     window w2 as (partition by deptno order by id,ename)
    ),
    tmp7 as
    (
    select 1 flag1,0 flag2,case when rn = 1 then deptno else concat(' ',ename) end it_dept
      from tmp6
      where rn <= cnt + 1
    ),
    tmp8 as
    (
    select flag1,
           flag2,
           it_dept
     from tmp7
    union all
    select flag1,
           flag2,
           it_dept
     from tmp4
    ),
    tmp9 AS
    (
    select flag1,
           flag2,
           it_dept,
           row_number() over w3 as 'rn2'
      from tmp8
     window w3 as ()
    ),
    tmp10 as
    (
    select sum(flag1) over (partition by flag2 order by flag1,rn2) flag,
           flag2,
           it_dept
      from tmp9
    )
    select max(case when flag2 = 0 then it_dept end) research,
           max(case when flag2 = 1 then it_dept end) apps
      from tmp10
     group by flag
     order by flag

测试记录:

mysql> with tmp1 as
        -> (
        -> select deptno,
        ->        ename,
        ->        count(*) over (partition by deptno) cnt
        -> from it_apps
        -> order by deptno,ename
        -> ),
        -> tmp2 as
        -> (
        -> select 1 id union select 2
        -> ),
        -> tmp3 as
        -> (
        -> select deptno,
        ->        ename,
        ->        cnt,
        ->        row_number() over w1 as 'rn'
        ->   from tmp1,tmp2
        -> window w1 as (partition by deptno order by id,ename)
        -> ),
        -> tmp4 as
        -> (
        -> select 1 flag1,
        ->        1 flag2,
        ->        case when rn = 1 then deptno else concat('  ',ename) end it_dept
        ->   from tmp3
        ->   where rn <= cnt + 1
        -> )
        -> ,
        -> tmp5 as
        -> (
        -> select deptno,
        ->        ename,
        ->        count(*) over (partition by deptno) cnt
        -> from it_research
        -> order by deptno,ename
        -> ),
        -> tmp6 as
        -> (
        -> select deptno,
        ->        ename,
        ->        cnt,
        ->        row_number() over w2 as 'rn'
        ->   from tmp5,tmp2
        ->  window w2 as (partition by deptno order by id,ename)
        -> ),
        -> tmp7 as
        -> (
        -> select 1 flag1,0 flag2,case when rn = 1 then deptno else concat('  ',ename) end it_dept
        ->   from tmp6
        ->   where rn <= cnt + 1
        -> ),
        -> tmp8 as
        -> (
        -> select flag1,
        ->        flag2,
        ->        it_dept
        ->  from tmp7
        -> union all
        -> select flag1,
        ->        flag2,
        ->        it_dept
        ->  from tmp4
        -> ),
        -> tmp9 AS
        -> (
        -> select flag1,
        ->        flag2,
        ->        it_dept,
        ->        row_number() over w3 as 'rn2'
        ->   from tmp8
        ->  window w3 as ()
        -> ),
        -> tmp10 as
        -> (
        -> select sum(flag1) over (partition by flag2 order by flag1,rn2) flag,
        ->        flag2,
        ->        it_dept
        ->   from tmp9
        -> )
        -> select max(case when flag2 = 0 then it_dept end) research,
        ->        max(case when flag2 = 1 then it_dept end) apps
        ->   from tmp10
        ->  group by flag
        ->  order by flag ;
    +--------------+--------------+
    | research     | apps         |
    +--------------+--------------+
    | 100          | 400          |
    |   JONES      |   CORRALES   |
    |   TONEY      |   MARQUEZ    |
    |   HOPKINS    |   MAYWEATHER |
    | 200          |   MOSLEY     |
    |   MORALES    |   CASTILLO   |
    |   P.WHITAKER | 500          |
    |   ROBINSON   |   GATTI      |
    |   MARCIANO   |   CALZAGHE   |
    | 300          | 600          |
    |   LACY       |   HAGLER     |
    |   WRIGHT     |   HEARNS     |
    |   J.TAYLOR   |   LAMOTTA    |
    | NULL         |   FRAZIER    |
    | NULL         | 700          |
    | NULL         |   JUDAH      |
    | NULL         |   MARGARITO  |
    | NULL         |   GUINN      |
    +--------------+--------------+
    18 rows in set (0.00 sec)

**这样看起来临时表都10个临时表了，逻辑看起来太复杂了，下面我们拆开来讲解**

## 2.1 分解求出it\_apps各部门及员工 ##

我们首先来看看tmp4的结果集:

那么tmp4的结果集是怎么来的呢？  
**我们来看看tmp1和tmp2以及tmp3**  
这个地方为什么要有tmp2，一个id为1 和 2 的表，其实因为第一行要显示deptno，后面的才是ename，所以此时应该是n+1，如果只是n，这个地方deptno带不出来。  
tmp3就是在tmp1和tmp2的基础上进行了加工，记住order by这个地方一定要正确，不然数据会不准确

tmp3加工完成后，根据每个deptno rn为1的则显示deptno，从2到n+1遍历ename，根据rn <= cnt + 1来进行控制

mysql> select deptno,
        ->        ename,
        ->        count(*) over (partition by deptno) cnt
        -> from it_apps
        -> order by deptno,ename ;
    +--------+------------+-----+
    | deptno | ename      | cnt |
    +--------+------------+-----+
    |    400 | CASTILLO   |   5 |
    |    400 | CORRALES   |   5 |
    |    400 | MARQUEZ    |   5 |
    |    400 | MAYWEATHER |   5 |
    |    400 | MOSLEY     |   5 |
    |    500 | CALZAGHE   |   2 |
    |    500 | GATTI      |   2 |
    |    600 | FRAZIER    |   4 |
    |    600 | HAGLER     |   4 |
    |    600 | HEARNS     |   4 |
    |    600 | LAMOTTA    |   4 |
    |    700 | GUINN      |   3 |
    |    700 | JUDAH      |   3 |
    |    700 | MARGARITO  |   3 |
    +--------+------------+-----+
    14 rows in set (0.00 sec)
    
    mysql> select 1 id union select 2 ;
    +----+
    | id |
    +----+
    |  1 |
    |  2 |
    +----+
    2 rows in set (0.00 sec)
    
    mysql> with tmp1 as
        -> (
        -> select deptno,
        ->        ename,
        ->        count(*) over (partition by deptno) cnt
        -> from it_apps
        -> order by deptno,ename
        -> ),
        -> tmp2 as
        -> (
        -> select 1 id union select 2
        -> )
        -> select deptno,
        ->        ename,
        ->        cnt,
        ->        row_number() over w1 as 'rn'
        ->   from tmp1,tmp2
        -> window w1 as (partition by deptno order by id,ename)
        -> ;
    +--------+------------+-----+----+
    | deptno | ename      | cnt | rn |
    +--------+------------+-----+----+
    |    400 | CASTILLO   |   5 |  1 |
    |    400 | CORRALES   |   5 |  2 |
    |    400 | MARQUEZ    |   5 |  3 |
    |    400 | MAYWEATHER |   5 |  4 |
    |    400 | MOSLEY     |   5 |  5 |
    |    400 | CASTILLO   |   5 |  6 |
    |    400 | CORRALES   |   5 |  7 |
    |    400 | MARQUEZ    |   5 |  8 |
    |    400 | MAYWEATHER |   5 |  9 |
    |    400 | MOSLEY     |   5 | 10 |
    |    500 | CALZAGHE   |   2 |  1 |
    |    500 | GATTI      |   2 |  2 |
    |    500 | CALZAGHE   |   2 |  3 |
    |    500 | GATTI      |   2 |  4 |
    |    600 | FRAZIER    |   4 |  1 |
    |    600 | HAGLER     |   4 |  2 |
    |    600 | HEARNS     |   4 |  3 |
    |    600 | LAMOTTA    |   4 |  4 |
    |    600 | FRAZIER    |   4 |  5 |
    |    600 | HAGLER     |   4 |  6 |
    |    600 | HEARNS     |   4 |  7 |
    |    600 | LAMOTTA    |   4 |  8 |
    |    700 | GUINN      |   3 |  1 |
    |    700 | JUDAH      |   3 |  2 |
    |    700 | MARGARITO  |   3 |  3 |
    |    700 | GUINN      |   3 |  4 |
    |    700 | JUDAH      |   3 |  5 |
    |    700 | MARGARITO  |   3 |  6 |
    +--------+------------+-----+----+
    28 rows in set (0.00 sec)

## 2.2 it\_apps与it\_research进行拼接 ##

tmp9得到如下结果:  
![image.png][image.png 1]

此时就可以知道 flag1和flag2的作用了，flag2用来区别是 apps还是research，flag1根据flag2的区别进行累计求和，然后根据新的flag来进行group by，这样就可以将apps和research进行展示了

tmp10返回如下结果:  
![image.png][image.png 2]

有了tmp10的结果，就很可以根据flag直接分组，通过max函数进行求求值。

[image.png]: /images/20221023/22528d3d15e146cdaeb0c47979d173ef.png
[image.png 1]: /images/20221023/264461500608429ba730c245cf446e4d.png
[image.png 2]: /images/20221023/9d703e11941c4aff946fcc5de4ded2ca.png