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POSQL Server : left join results in fewer rows than in left table
 

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    <p>I am using SQL Server (I believe it is 2005).</p> <p>I have <code>TableA</code> that has 2 columns and 439 rows (each row is unique). </p> <pre><code>+----------+ |ID | Name | +----------+ </code></pre> <p>I have <code>TableB</code> that has 35 columns and many hundreds of thousand rows (each row is also unique). </p> <pre><code>+------------------------------------------------------------------------------+ |Date | ID | Name | Blah1 | Blah2 | ... | Hour1 | Hour2 | Hour3 | ... | Hour24 | +------------------------------------------------------------------------------+ </code></pre> <p>Each row in <code>TableB</code> has hourly observations and some other house keeping information. Now for testing purposes I am only interested in today's date i.e 4/19/2013. </p> <p>If I do:</p> <pre><code>Select count(*) from TableB where Date = '4/19/2013 12:00:00 AM' </code></pre> <p>I get 10526, which is correct as there are 10526 distinct locations for which there is hourly observation data each day. </p> <p>I want to LEFT JOIN TableA and TableB <code>on a.id = b.id</code>, which SHOULD produce a result that has 439 rows. </p> <p>Unfortunately, the result has 246 rows. How can this be? Isn't a <code>LEFT JOIN</code> suppose to return all rows in <code>TableA</code> regardless of whether there was a match in <code>TableB</code>? </p> <p>*<strong><em>EDIT</em>*</strong></p> <p>The complete query I used was:</p> <pre><code>select * from TableA as a left join TableB as b on a.id = b.id where RealDate = '4/20/2013 12:00:00 AM' </code></pre>
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    1. UScodingknob
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    1. COcan u show complete query you used
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    2. CO@PSR - I have edited my original post to include the original query used.
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      1. UScodingknob
 

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