Question

加入三个表并计算

表部

mid  m_name
1    Health
2    Telecom
3    Economic

表DocumentDetail

id  m_id doc_type 
1    3    1
2    1    2
3    2    3
4    3    2
5    2    4
6    3    1

表类型：

dID   d_name
1     pdf
2     xls
3     doc
4     png
5     zip

我想像这样放

m_name   pdf  xls  doc  png  zip
health   0    1    0    0    0
Telecom  0    0    1    1    0
Economic 2    1    0    0    0

我们可以像这样查询输出吗？提前谢谢。

Answer 1

SELECT m_name,(SUM(CASE doc_type WHEN 1 THEN 1 ELSE 0 END)) as pdf,
      (SUM(CASE doc_type WHEN 2 THEN 1 ELSE 0 END)) AS xls,
      (SUM(CASE doc_type WHEN 3 THEN 1 ELSE 0 END)) AS doc,
      (SUM(CASE doc_type WHEN 4 THEN 1 ELSE 0 END)) AS png,
      (SUM(CASE doc_type WHEN 5 THEN 1 ELSE 0 END)) AS zip
FROM  Ministry INNER JOIN DocumentDetail ON Ministry.`mid` = DocumentDetail.`m_id`
GROUP BY m_name

点击此SQL Fiddle 希望这有帮助

Answer 2

如果doc_type的数量是固定的，那么您可以尝试以下查询，否则您可能需要尝试动态SQL查询。

<强>查询

select t1.m_name,
count(case t2.doc_type when 1 then 1 end) as pdf,
count(case t2.doc_type when 2 then 1 end) as xls,
count(case t2.doc_type when 3 then 1 end) as doc,
count(case t2.doc_type when 4 then 1 end) as png,
count(case t2.doc_type when 5 then 1 end) as zip
from Ministry t1
join DocumentDetail t2
on t1.mid = t2.m_id
group by t1.m_name;

Answer 3

如果类型的数量会随着时间的推移而变化，请使用此解决方案：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      ', SUM(CASE dd.doc_type when ', dID,
      ' then 1 else 0 END) AS ', d_name, ' ')
  SEPARATOR '') INTO @sql
FROM Type;

SET @sql = CONCAT(
  'SELECT m.m_name', 
  @sql, 
  'FROM 
  Ministry AS m
  INNER JOIN DocumentDetail AS dd ON (m.mid = dd.m_id)
  GROUP BY m.m_name
  ORDER BY m.m_name'
);

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

输出：

m_name      pdf xls doc png zip
Economic    2   1   0   0   0
Health      0   1   0   0   0
Telecom     0   0   1   1   0

MySql将三个表连接在一起并计算行

3 个答案: