Re: Can someone explain this?

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From: Anith Sen (anith_at_bizdatasolutions.com)
Date: 09/16/04 

Date: Thu, 16 Sep 2004 14:17:42 -0500

In your second case, FromTtwo is used as an alias for the column ToneId. So
essentially your query is equivalent to:

SELECT * FROM Tone WHERE ToneId IN ( SELECT ToneId )

which due to lack of scoped aliasing, SQL Server identifies as :

SELECT * FROM Tone
 WHERE Tone.ToneId IN ( SELECT Tone.ToneId )

which is evaluated as:

SELECT * FROM Tone
 WHERE Tone.ToneId = Tone.ToneId ; 

-- 
Anith