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POIs converting everything to varbinary the correct way to compare character data?
 

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  1. POIs converting everything to varbinary the correct way to compare character data?
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    <p>I was using a MIN function to compare character data in a column that allowed nulls, with disastrous results. ;-) Here's a much simplified example that shows the same kind of thing:</p> <ol> <li><p>Determine the number of rows in sys.indexes:</p> <pre><code>select count(*) from sys.indexes; </code></pre></li> <li><p>Run this SQL:</p> <pre><code>select count(name), substring(cast(min(name) as varbinary),1,1) from sys.indexes; </code></pre> <p>If count matches #1, stop here. Try a different database (with more objects) instead.</p></li> <li><p>Go to the Messages tab. You should see: Warning: Null value is eliminated by an aggregate or other SET operation.</p></li> <li><p>How would you handle the nulls in the "name" column in order to resolve that Warning? with coalesce?</p></li> <li><p>Replace "name" with "coalesce(name,char(0x7e))" and run the SQL:</p> <pre><code>select count(coalesce(name,char(0x7e))), substring(cast(min(coalesce(name,char(0x7e))) as varbinary),1,1) from sys.indexes; </code></pre></li> <li><p>Note the result of the MIN function in #5 (0x7e rather than 0x63).</p></li> </ol> <p>Questions:</p> <p>A. Is coalesce the proper way to handle the Warning and missing (null) data per #4?</p> <p>B. Since the result in #6 is not what's expected, what is the correct way to compare character data in SQL Server? Convert everything to varbinary?</p> <p>[Edited...]</p> <p>In the discussions below, there was some confusion and discussion about the relationship between the null replacement via COALESCE and the results of the comparisons. The relationship between the two is this: when you select a string (including a single character) as a null replacement placeholder (steps #4 and #5 above), that string must satisfy the expected results of the comparison(s) that are being performed against values of other data in the query. With some collations, finding a suitable string may be more difficult than with other collations.</p>
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    1. USRob at TVSeries.com
    1. USRob at TVSeries.com
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    1. COJust ignore the warning. It is only there as an information message. You shouldn't cast to `varbinary` to compare character data.
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      1. USMartin Smith
    2. COIf you ignore the warning, the counts are off. That's what got my attention in the first place, in the original code, which is quite a bit more involved.
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      1. USRob at TVSeries.com
    3. CO`COUNT(col)` only counts `NOT NULL` values. Use `COUNT(*)` to count rows. I don't see how that in any way relates to comparing character data, can you tell us the original issue you were having?
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      1. USMartin Smith
 

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