Question

我已经看过这个问题（Please help merging 4 MySQL queries to One）希望它会有所帮助，但事实并非如此。我无法理解它，因为我的大脑已经油炸了。

我试图将四个SELECT语句合并为一个单独的单个SELECT语句。

字段是;

QUANTITY：INT;

ORDERDATE：DATE; //不是日期时间 - 我不需要时间。

MySQL版本5.6.17

我检索的数据是;

1）本财政年度订购的产品数量;

SELECT SUM(QUANTITY) AS YTD
  FROM ORDERDETAILS
  WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16"

请注意，在澳大利亚，财政年度是7月1日至6月30日。

2）本月订购的产品数量;

SELECT SUM(QUANTITY) AS MONTHY
  FROM ORDERDETAILS
  WHERE ORDERDATE BETWEEN "2017-02-01" AND "2017-02-16"

3）今天订购的产品数量;

SELECT SUM(QUANTITY) AS TODAYS
  FROM ORDERDETAILS
  WHERE ORDERDATE = "2017-02-16"

4）每个订单的平均订购产品数量

SELECT AVG(QUANTITY) AS BOOGER
  FROM ORDERDETAILS
  WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16"

我想避免向服务器发送四个单独的语句。也许它无法完成，但如果我能在单一陈述中取得同样的结果，我会感到高兴。

我看过联接，在选择中嵌入选择，但无法理解它。

一旦我获得数据，我所做的就是更新表格上的几个标签（Delphi）。

近55岁的大脑可以处理的任何提示都将受到赞赏。

Answer 1

您可以使用条件时执行此操作：

 select 
      sum(case when ORDERDATE BETWEEN '2016-07-01' AND '2017-02-16' then QUANTITY end ) as  YTD,
      sum(case when ORDERDATE BETWEEN '2017-02-01' AND '2017-02-16' then QUANTITY end ) as  MONTHY,
      sum(case when ORDERDATE = '2017-02-16' then QUANTITY end ) as  TODAYS,
      AVG(case when ORDERDATE BETWEEN '2016-07-01' AND '2017-02-16' then QUANTITY end ) as  BOOGER
       FROM ORDERDETAILS

Answer 2

您只需对表的不同调用使用不同的别名，并将其全部放在一个SELECT语句中，如下所示：

SELECT SUM(od1.QUANTITY) AS YTD,
       SUM(od2.QUANTITY) AS MONTHLY,
       SUM(od3.QUANTITY) AS TODAYS,
       AVG(od4.QUANTITY) AS BOOGER
FROM ORDERDETAILS od1,
     ORDERDETAILS od2,
     ORDERDETAILS od3,
     ORDERDETAILS od4
WHERE od1.ORDERDATE BETWEEN CAST('2016-07-01' AS DATE) AND CAST('2017-02-16' AS DATE)
  AND od2.ORDERDATE BETWEEN CAST('2017-02-01' AS DATE) AND CAST('2017-02-16' AS DATE)
  AND od3.ORDERDATE = CAST('2017-02-16' AS DATE)
  AND od4.ORDERDATE BETWEEN CAST('2016-07-01' AS DATE) AND CAST('2017-02-16' AS DATE)

Answer 3

使用SUM(IF())模式并在IF内移动条件。

SELECT 
  SUM(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", QUANTITY, 0)) AS YTD,
  SUM(IF(ORDERDATE BETWEEN "2017-02-01" AND "2017-02-16", QUANTITY, 0)) AS MONTHY,
  SUM(IF(ORDERDATE = "2017-02-16", QUANTITY, 0)) AS TODAYS,
  SUM(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", QUANTITY, 0)) / COUNT(IF(ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16", 1, NULL)) AS BOOGER
FROM ORDERDETAILS
WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16";

考虑使用CURDATE()作为今天的日期。

还可以添加WHERE子句，以便不扫描表的所有行，例如WHERE ORDERDATE BETWEEN "2016-07-01" AND "2017-02-16"之后FROM ORDERDETAILS

合并多个MySQL SELECT语句计算字段

3 个答案: