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Alias scope in SQL query

Posted on 2014-01-15
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Last Modified: 2014-01-16
Why is it that once an alias is declared for the table that the fully qualified name can no longer be used? I find this curious and am just interested if anyone has any insight into why this is or if this is just T-SQL.

Seems like a scope issue, that once an alias is declared below for the tables (i and p) that the fully qualified names are no longer valid.

Thanks.

USE AdventureWorks2012;
GO
SELECT i.SalesOrderDetailID
FROM SalesLT.SalesOrderDetail AS i
INNER JOIN SalesLT.SalesOrderHeader AS p
ON SalesLT.SalesOrderDetail.SalesOrderID = SalesLT.SalesOrderDetail.SalesOrderID

results in an error

but
USE AdventureWorks2012;
GO
SELECT SalesOrderDetailID
FROM SalesLT.SalesOrderDetail
INNER JOIN SalesLT.SalesOrderHeader
ON SalesLT.SalesOrderDetail.SalesOrderID = SalesLT.SalesOrderDetail.SalesOrderID

is fine
and this is also fine

USE AdventureWorks2012;
GO
SELECT i.SalesOrderDetailID
FROM SalesLT.SalesOrderDetail AS i
INNER JOIN SalesLT.SalesOrderHeader AS p
ON i.SalesOrderID = p.SalesOrderID
0
Comment
Question by:alexmac05
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3 Comments
 
LVL 32

Expert Comment

by:awking00
ID: 39782924
One of the primary reasons for using an alias is so you don't have to use the fully qualified name and why would you create an alias if you're not going to use it?
0
 
LVL 70

Accepted Solution

by:
Qlemo earned 500 total points
ID: 39783047
This is a general "feature" of all SQL dialects I know of, and not restricted to T-SQL. Once you introduce an alias, you can't use the real name. That is because you rename the internal object name. It isn't just an alias, it is the name.
0
 

Author Comment

by:alexmac05
ID: 39785670
Thank you to both of you for answering.
0

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