Question

通过此查询，我得到了2列不同的值

SELECT DISTINCT 
    Transport.ID, Transport.Address 
FROM  
    Cars 
LEFT JOIN 
    Transport ON Cars.TransportFrom=Transport.ID 
ORDER BY 
    address

现在我需要再添一个列：

SUM(CASE WHEN Active='True' THEN 1 ELSE 0 END)

但是如果我做像

这样的查询，我会收到错误

SELECT DISTINCT 
    Transport.ID, Transport.Address, 
    SUM(CASE WHEN Active = 'True' THEN 1 ELSE 0 END)
FROM 
    Cars 
LEFT JOIN 
    Transport ON Cars.TransportFrom = Transport.ID 
ORDER BY 
    address

Msg 8120，Level 16，State 1，Line 1
列'Transport.ID'在选择列表中无效，因为它不包含在聚合函数或GROUP BY子句中。

SELECT 
    Transport.ID, Transport.Address, 
    SUM(CASE WHEN Active = 'True' THEN 1 ELSE 0 END)
FROM 
    Cars 
LEFT JOIN 
    Transport ON Cars.TransportFrom = Transport.ID 
ORDER BY 
    address
GROUP BY 
    ID

Msg 156，Level 15，State 1，Line 5
关键字“GROUP”附近的语法不正确。

SELECT 
    Transport.ID, Transport.Address, 
    SUM(CASE WHEN Active = 'True' THEN 1 ELSE 0 END)
FROM 
    Cars 
LEFT JOIN 
    Transport ON Cars.TransportFrom = Transport.ID 
GROUP BY 
    ID
ORDER BY 
    address

Msg 209，Level 16，State 1，Line 4
不明确的列名称'ID'。

SELECT 
    Transport.ID, Transport.Address, 
    SUM(CASE WHEN Active = 'True' THEN 1 ELSE 0 END)
FROM 
    Cars 
LEFT JOIN 
    Transport ON Cars.TransportFrom = Transport.ID 
GROUP BY 
    Transport.ID
ORDER BY 
    address

Msg 8120，Level 16，State 1，Line 1
列'Transport.address'在选择列表中无效，因为它不包含在聚合函数或GROUP BY子句中。

如何正确理解语法？

Answer 1

错误信息是否清楚，没有？

SELECT Transport.ID, Transport.Address, SUM(CASE WHEN Active='True' THEN 1 ELSE 0 END)
FROM Cars 
LEFT JOIN Transport ON Cars.TransportFrom=Transport.ID 
--add all the fields from select clause which are not in an aggregation function
GROUP BY Transport.ID, Transport.Address 
ORDER BY address

在SQL Server中使用GROUP BY

1 个答案: