一个`Select`查询生成12个结果集答案

【问题标题】：One `Select` query to generate 12 result sets一个`Select`查询生成12个结果集
【发布时间】：2014-11-16 01:51:57
【问题描述】：

我有一个名为 VAT 的表格，我需要生成每月的 VAT 报告。所以下面是我要做的......

    SELECT SUM(Amount) AS "January" 
    WHERE current_time_stamp BETWEEN '2014-01-01' AND '2014-01-310'
    FROM VAT

就像上面的查询一样，我有 12 个查询 1 月、2 月、3 月等。那么，不是写 12 个，有没有办法可以在 1 个查询中得到所有这些？

【问题讨论】：

标签： mysql sql database select

【解决方案1】：

使用GROUP BY，像这样：

SELECT SUM(Amount), MONTH(current_time_stamp) AS `Month` 
FROM VAT
WHERE current_time_stamp BETWEEN '2014-01-01' AND '2014-12-31'
GROUP BY MONTH(current_time_stamp)

但是，如果您有很多记录，它可能会很慢。

【讨论】：

【解决方案2】：

类似的东西会延长到十二个月

SELECT MAX(X.January) AS January, MAX(X.February) AS February FROM
(
SELECT SUM(Amount) AS January, 0 AS February
    WHERE current_time_stamp BETWEEN '2014-01-01' AND '2014-01-31'
    FROM VAT
UNION
SELECT 0 AS January, SUM(Amount) AS February
    WHERE current_time_stamp BETWEEN '2014-02-01' AND '2014-02-29'
    FROM VAT
) X

或者你也可以这样做：

SELECT 'January' AS Month, SUM(Amount) AS Amount
    WHERE current_time_stamp BETWEEN '2014-01-01' AND '2014-01-31'
    FROM VAT
UNION
 SELECT 'February' AS Month, SUM(Amount) AS Amount
    WHERE current_time_stamp BETWEEN '2014-02-01' AND '2014-02-29'
    FROM VAT

【讨论】：

【解决方案3】：

您可以在 case 语句中使用条件求和，下面的查询将为您提供一行 12 列的每月总和

SELECT 
   SUM(case when current_time_stamp BETWEEN '2014-01-01' AND '2014-01-31' then Amount else 0 end) AS `January` ,
   SUM(case when current_time_stamp BETWEEN '2014-02-01' AND '2014-02-29' then Amount else 0 end) AS `Febuary` ,
   .
   .
   .
   SUM(case when current_time_stamp BETWEEN '2014-12-01' AND '2014-12-31' then Amount else 0 end) AS `December` 
 FROM VAT

【讨论】：

【解决方案4】：

select t.mnth_amt,t.mnth 
from (
     select sum(amount) as mnth_amt,MONTH(current_time_stamp ) as mnth from vat where current_time_stamp BETWEEN '2014-01-01' AND  
     '2014-12-31' GROUP BY MONTH(current_time_stamp) 
     ) t order by mnth

【讨论】：