Question

SQL相当新，但我试图从同一个表中获得2个选择查询之间的区别。我试过以下

SELECT
(SELECT KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date FROM Energiemeters WHERE Date = '2017-05-01')
 -
(SELECT KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date FROM Energiemeters WHERE Date = '2017-04-01') AS Difference

但我最终得到以下错误：

 #1241 - Operand should contain 1 column(s)

Answer 1

如果您想要5月1日但不是4月1日的行，那么一种方法是使用聚合：

SELECT KwhMeter, IndexElek, CalorieMeter, IndexWarmte, IndexWarmWater, IndexKoudWater, Date
FROM Energiemeters
WHERE Date IN ('2017-04-01', '2017-05-01')
GROUP BY KwhMeter, IndexElek, CalorieMeter, IndexWarmte, IndexWarmWater, IndexKoudWater
HAVING MIN(Date) = '2017-05-01';

Answer 2

使用Cross Join。这是假设每个日期只得到一行。

Select 
(a.KwhMeter-b.KwhMeter) as KwhMeter,
(a.IndexElek-b.IndexElek) as IndexElek,
(a.CalorieMeter-b.CalorieMeter) CalorieMeter,
(a.IndexWarmte-b.IndexWarmte) IndexWarmte,
(a.IndexWarmWater-b.IndexWarmWater) IndexWarmWater,
(a.IndexKoudWater-b.IndexKoudWater) IndexKoudWater,
(a.Date-b.Date) as Date
from
(
SELECT distinct KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date 
FROM Energiemeters 
WHERE Date = '2017-05-01' 
) a
cross join
(
SELECT distinct KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date 
FROM Energiemeters 
WHERE Date = '2017-04-01' 
) b;

Answer 3

好像你想从日期2017-05-01和2017-04-01确定的两行中减去相应的列值？

如果是，则查询可以写成如下：

SELECT SUM(CASE Date 
               WHEN '2017-05-01' THEN KwhMeter
               WHEN '2017-04-01' THEN -KwhMeter
           END) AS KwhMeter,
       SUM(CASE Date 
               WHEN '2017-05-01' THEN IndexElek
               WHEN '2017-04-01' THEN -IndexElek
           END) AS IndexElek, 
       SUM(CASE Date 
               WHEN '2017-05-01' THEN CalorieMeter
               WHEN '2017-04-01' THEN -CalorieMeter
           END) AS CalorieMeter,
       SUM(CASE Date 
               WHEN '2017-05-01' THEN IndexWarmte
               WHEN '2017-04-01' THEN -IndexWarmte
           END) AS IndexWarmte,
       SUM(CASE Date 
               WHEN '2017-05-01' THEN IndexWarmWater
               WHEN '2017-04-01' THEN -IndexWarmWater
           END) AS IndexWarmte, 
       SUM(CASE Date 
               WHEN '2017-05-01' THEN IndexKoudWater 
               WHEN '2017-04-01' THEN -IndexKoudWater 
           END) AS IndexKoudWater
FROM Energiemeters
WHERE Date IN ('2017-05-01', '2017-04-01')

可以找到小型工作演示here。

Answer 4

在大多数RDBMS中工作，除了MYSQL：

如果我想计算每列差异，我会使用公共表表达式来准备子结果，然后计算差异。

WITH 
res1 AS
(SELECT KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date FROM Energiemeters WHERE Date = '2017-05-01'),
res2 AS
(SELECT KwhMeter,IndexElek,CalorieMeter,IndexWarmte,IndexWarmWater,IndexKoudWater,Date FROM Energiemeters WHERE Date = '2017-04-01')
SELECT
r1.KwhMeter - r2.KwhMeter, r1.OtherColumnName - r2.OtherColumnName ... FROM res1 r1, res2 r2

但是......每个子选择（日期）一行完美。你是否保证每个日期有一个条目？那是PK吗？您需要指定您的问题，主要是“差异”是什么意思。

尝试计算SQL中2个选择查询之间的差异

4 个答案: