旧式 JOIN 语法在 T-SQL 中是啥意思？

Posted 2023-02-24

【中文标题】旧式 JOIN 语法在 T-SQL 中是啥意思？

【英文标题】：What does the old-style JOIN syntax mean in T-SQL?旧式 JOIN 语法在 T-SQL 中是什么意思？

【发布时间】：2016-03-02 09:04:50

【问题描述】：

我需要编辑旧式 T-SQL 代码。

=* 是什么意思？

*= 是什么意思？

我认为，它们是 JOIN，但我不知道它们每个是什么 JOIN 类型。

【问题讨论】：

那些是外连接

它们之间有什么区别？

一个是左连接，另一个是右连接。详见手册msdn.microsoft.com/en-us/library/…

【参考方案1】：

我找到答案了！

-- Example 1: Deprecated syntax for an inner join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] T2, [dbo].[Table1] T1 
WHERE [T1].[ID] = [T2].[ID]

-- Example 2: Current syntax for an inner join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] AS T2
INNER JOIN [dbo].[Table1] as T1
ON [T2].[ID] = [T2].[ID]

-- Example 3: Deprecated syntax for a left outer join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] T2, [dbo].[Table1] T1 
WHERE [T1].[ID] *= [T2].[ID]

-- Example 4: Fixed syntax for a left outer join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] AS T2
LEFT OUTER JOIN [dbo].[Table1] as T1
ON [T2].[ID] = [T2].[ID]

-- Example 5: Deprecated syntax for a right outer join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] T2, [dbo].[Table1] T1 
WHERE [T1].[ID] =* [T2].[ID]

-- Example 6: Fixed syntax for a right outer join
SELECT [T2].[c3], [T1].[c3] 
FROM [dbo].[Table2] AS T2
RIGHT OUTER JOIN [dbo].[Table1] as T1
ON [T2].[ID] = [T2].[ID]

https://msdn.microsoft.com/en-us/library/dd172122(v=vs.100).aspx

【讨论】：

这里有明显的错别字：[T2].[ID] = [T2].[ID]。 MSDN 并不完美。