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POSimplifying (aliasing) T-SQL CASE statements. Any improvement possible?
 

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    <p>As you can see, this sucks big time. Any alternative? I've tried using the column alias in the group by clause to no avail.</p> <pre><code>select count(callid) , case when callDuration &gt; 0 and callDuration &lt; 30 then 1 when callDuration &gt;= 30 and callDuration &lt; 60 then 2 when callDuration &gt;= 60 and callDuration &lt; 120 then 3 when callDuration &gt;= 120 and callDuration &lt; 180 then 4 when callDuration &gt;= 180 and callDuration &lt; 240 then 5 when callDuration &gt;= 240 and callDuration &lt; 300 then 6 when callDuration &gt;= 300 and callDuration &lt; 360 then 7 when callDuration &gt;= 360 and callDuration &lt; 420 then 8 when callDuration &gt;= 420 and callDuration &lt; 480 then 9 when callDuration &gt;= 480 and callDuration &lt; 540 then 10 when callDuration &gt;= 540 and callDuration &lt; 600 then 11 when callDuration &gt;= 600 then 12 end as duration from callmetatbl where programid = 1001 and callDuration &gt; 0 group by case when callDuration &gt; 0 and callDuration &lt; 30 then 1 when callDuration &gt;= 30 and callDuration &lt; 60 then 2 when callDuration &gt;= 60 and callDuration &lt; 120 then 3 when callDuration &gt;= 120 and callDuration &lt; 180 then 4 when callDuration &gt;= 180 and callDuration &lt; 240 then 5 when callDuration &gt;= 240 and callDuration &lt; 300 then 6 when callDuration &gt;= 300 and callDuration &lt; 360 then 7 when callDuration &gt;= 360 and callDuration &lt; 420 then 8 when callDuration &gt;= 420 and callDuration &lt; 480 then 9 when callDuration &gt;= 480 and callDuration &lt; 540 then 10 when callDuration &gt;= 540 and callDuration &lt; 600 then 11 when callDuration &gt;= 600 then 12 end </code></pre> <p>EDIT: I really meant to ask how to have a single case source, but case modifications are welcome anyway (although less useful because the intervals probably will be modified and might even be automatically generated). </p> <p>As has been considered by some people, callDuration is indeed a float so some listed solutions are not valid for my use case, by leaving values out of the intervals.</p> <p>Lessons:</p> <ul> <li><p>Look for patterns in the case expression to reduce it if possible and worthwhile</p> <pre><code> case when callDuration &gt; 0 AND callDuration &lt; 30 then 1 when callDuration &gt; 600 then 12 else floor(callDuration/60) + 2 end end as duration </code></pre></li> <li><p>Use inline views to have a single source of the case</p> <pre><code>select count(d.callid), d.duration from ( select callid , case when callDuration &gt; 0 AND callDuration &lt; 30 then 1 when callDuration &gt; 600 then 12 else floor(callDuration/60) + 2 end end as duration from callmetatbl where programid = 1001 and callDuration &gt; 0 ) d group by d.duration </code></pre></li> <li><p>Or use common table expressions</p> <pre><code> with duration_case as ( select callid , case when callDuration &gt; 0 AND callDuration &lt; 30 then 1 when callDuration &gt; 600 then 12 else floor(callDuration/60) + 2 end end as duration from callmetatbl where programid = 1001 and callDuration &gt; 0 ) select count(callid), duration from duration_case group by duration </code></pre></li> <li><p>Or use an user defined function (no example so far :-) )</p></li> <li><p>Or use a lookup table and a join</p> <pre><code>DECLARE @t TABLE(durationFrom float, durationTo float, result INT) --populate table with values so the query works select count(callid) , COALESCE(t.result, 12) from callmetatbl JOIN @t AS t ON callDuration &gt;= t.durationFrom AND callDuration &lt; t.durationTo where programid = 1001 and callDuration &gt; 0 </code></pre></li> </ul> <p>Thanks to everybody and I'm having a very difficult time choosing an accepted answer, as many covered different parts of the question (and I was there thinking it was a simple question with a straightforward answer :-), sorry for the confusion).</p>
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    1. COif the question is "how do I alias a complex expression so I can reference it in a GROUP BY clause", one approach is to use an inline view (see my answer), or a view definition stored in the database). the _other_ question (everyone else seems to be answering) is "how do I simplify this particular expression", there's several approaches to that as well.
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    2. CO@vinko: i've updated my answer to include an example user defined function (just a scalar function to replace the inline expression). a table valued function could be used to return a lookup table... that's a workable approach as well. BE CAREFUL of gaps and overlaps using lookup tables and join conditions (the potential for rows to be dropped and/or duplicated.) Consider what's going to need to be TESTED vs. the need for flexibility. (In my experience, it takes more effort to _test_ code than it does to _write_ code.)
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    3. CO@vinko: ALSO consider specifying each "breakpoint" value only once (use only one bound, and the guarantee of an early return when a condition is satisfied.) I infer the specification that every callDuration (>0) should fall into a bucket, and not be lost in a gap between two buckets.
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