计算另一个 table 中存在的值并旋转结果

Question

我想计算个来自Chat table 的值：

ID    REASON_ID    DEPARTMENT_ID    
 1      46           1
 2      46           1
 3      50           1
 4      50           2
 5      100          1 
 6      100          2

那些存在于 Reason table :

ID    REASON_NAME
46    Reason1
50    Reason2
100   Reason3

其中 DEPARTMENT_ID=1，我想要这样的结果：

ID46  ID50  ID100
 2      1     1

我该怎么做？

Answer 1

您可以尝试以下方法：

set @sql = null;
select group_concat( distinct
  concat( ' sum(r.id= ', r.id,') as ID', r.id )
) into @sql
from Chat c
join Reason r on c.reason_id = r.id 
where c.department_id = 1;

set @sql = concat('select ',@sql, ' 
from Chat c
join Reason r on c.reason_id = r.id 
where c.department_id = 1');

prepare stmt from @sql;
execute stmt;
deallocate prepare stmt;

SQLFiddle

Answer 2

动态 SQL 解决方案要好得多，但如果您需要其他选择：

SELECT SUM(I46) ID46,
SUM(I50) ID50,
SUM(I100) ID100
FROM
(SELECT 
COUNT(CASE WHEN reason_id = 46 THEN 1 END) I46,
COUNT(CASE WHEN reason_id = 50 THEN 1 END) I50,
COUNT(CASE WHEN reason_id = 100 THEN 1 END) I100
FROM chat
WHERE department_id = 1
GROUP BY reason_id) q1;

计算另一个 table 中存在的值并旋转结果

Count values that exist in another table and pivot the result

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count