mysql - 子查询

Question

我有这张 table

我想要并且可以让它看起来像这样

我使用的查询是这样的 {

SELECT  Cat,Reg,Branch, Mnth, Qty
FROM
(
  SELECT Cat,Reg,Branch, 'Jan' Mnth, Jan Qty
  FROM BQV
  WHERE Jan > 0
  UNION ALL
  SELECT Cat,Reg,Branch, 'Feb', Feb
  FROM BQV

  UNION ALL
  SELECT Cat,Reg,Branch, 'Mar', Mar
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Apr', Apr
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'May', May
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Jun', Jun
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Jul', Jul
  FROM BQV
  WHERE Feb > 0

  UNION ALL
  SELECT Cat,Reg,Branch, 'Aug', Aug
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Sept', Sep
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Oct', Octo
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Nov', Nov
  FROM BQV

UNION ALL
  SELECT Cat,Reg,Branch, 'Dec', Dece
  FROM BQV

) QV

}

我可以通过 View 或存储过程或其他方式实现此目的吗？ 我的 MySQL 版本是 5.5，它不能在 View 中包含子查询，而且我无法升级我的数据库，因为我无法承受任何损失或错误。

Answer 1

您不需要派生表(MySQL 错误地将其命名为子查询)，只需将其删除即可:

CREATE VIEW foo AS
SELECT Cat,Reg,Branch, 'Jan' AS Mnth, Jan AS Qty
FROM BQV
WHERE Jan > 0

UNION ALL
SELECT Cat,Reg,Branch, 'Feb', Feb
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Mar', Mar
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Apr', Apr
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'May', May
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Jun', Jun
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Jul', Jul
FROM BQV
WHERE Feb > 0

UNION ALL
SELECT Cat,Reg,Branch, 'Aug', Aug
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Sept', Sep
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Oct', Octo
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Nov', Nov
FROM BQV

UNION ALL
SELECT Cat,Reg,Branch, 'Dec', Dece
FROM BQV

另一个解决方案基于对存储月份名称“Jan”到“Dec”的第二个表的CROSS JOIN:

create table months ( mnth char(3));
insert into months values ('Jan'),('Feb'),...

select Cat,Reg,Branch, months.mnth, 
   case mnth 
     when 'Jan' then Jan
     when 'Feb' then Feb
     ...
     when 'Dec' then Dece
   end
from BQV CROSS JOIN months