多个独立输出的多个 SELECT 语句

Question

我在 SQL Server 中有一个数据库，列出了包含每个事件日期的海事事件。 对于图表说明，我现在想编写一个 SQL 语句（用于 Visual Studio），它给出了每年的事件总数。

例子：

2009 年 2010 年（年 - X 轴）

4575 5432（年 - Y 轴）

X轴的SELECT语句，我可以这样写

SELECT year1, year2 FROM (SELECT 2009 AS year1) AS a, ( SELECT 2010 AS year2) AS b

但是第二个呢？ 当我写类似的东西时：

SELECT totalyear1, totalyear2 FROM (SELECT COUNT(Reference) FROM STO.dbo.STOMaritimeIncidents WHERE [Incident date] = 2010 AS totalyear1) AS a, (SELECT COUNT(Reference) FROM STO.dbo.STOMaritimeIncidents WHERE [Incident date] = 2009 AS totalyear2) AS b

我收到类似“Msg 156, Level 15, State 1, Line 1 关键字 'AS' 附近的语法不正确。"

如果有人能给我解释或帮助我，我将不胜感激。非常感谢！

Answer 1

AS totalyear1 和 AS totalyear2 别名声明需要在列本身上进行：

SELECT totalyear1, totalyear2 
FROM (SELECT COUNT(Reference) AS totalyear1 
      FROM STO.dbo.STOMaritimeIncidents 
      WHERE [Incident date] = 2010) AS a, 
     (SELECT COUNT(Reference) AS totalyear2 
      FROM STO.dbo.STOMaritimeIncidents 
      WHERE [Incident date] = 2009) AS b

您可以通过简单地在一个查询中执行此操作来改进这一点：

SELECT SUM(CASE WHEN [Incident date] = 2010 THEN 1 ELSE 0) as totalyear1,
       SUM(CASE WHEN [Incident date] = 2009 THEN 1 ELSE 0) as totalyear2
FROM STO.dbo.STOMaritimeIncidents

如果您不介意（或更喜欢）旋转数据，您可以使用@Umair 的建议并将 COUNT 与 GROUP BY 子句一起使用。

Answer 2

P.s 您可以在一个查询中完成所有操作！比如

SELECT [Incident date], Total = COUNT(Reference) 
FROM STO.dbo.STOMaritimeIncidents
GROUP BY [Incident date]
WHERE [Incident date] IN (2009, 2010)

至于您的实际错误，是因为...WHERE [Incident date] = 2009 AS totalyear2 等行。它需要采用以下格式（别名需要在列上）

SELECT totalyear2 = COUNT(Reference) FROM STO.dbo.STOMaritimeIncidents WHERE [Incident date] = 2010