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

Question

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.

select count(callid) ,
case
        when callDuration > 0 and callDuration < 30 then 1
        when callDuration >= 30 and callDuration < 60 then 2
        when callDuration >= 60 and callDuration < 120 then 3
        when callDuration >= 120 and callDuration < 180 then 4
        when callDuration >= 180 and callDuration < 240 then 5
        when callDuration >= 240 and callDuration < 300 then 6
        when callDuration >= 300 and callDuration < 360 then 7
        when callDuration >= 360 and callDuration < 420 then 8
        when callDuration >= 420 and callDuration < 480 then 9
        when callDuration >= 480 and callDuration < 540 then 10
        when callDuration >= 540 and callDuration < 600 then 11
        when callDuration >= 600 then 12
end as duration
from callmetatbl
where programid = 1001 and callDuration > 0
group by case
        when callDuration > 0 and callDuration < 30 then 1
        when callDuration >= 30 and callDuration < 60 then 2
        when callDuration >= 60 and callDuration < 120 then 3
        when callDuration >= 120 and callDuration < 180 then 4
        when callDuration >= 180 and callDuration < 240 then 5
        when callDuration >= 240 and callDuration < 300 then 6
        when callDuration >= 300 and callDuration < 360 then 7
        when callDuration >= 360 and callDuration < 420 then 8
        when callDuration >= 420 and callDuration < 480 then 9
        when callDuration >= 480 and callDuration < 540 then 10
        when callDuration >= 540 and callDuration < 600 then 11
        when callDuration >= 600 then 12
end

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).

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.

Lessons:

• Look for patterns in the case expression to reduce it if possible and worthwhile

   case
      when callDuration > 0 AND callDuration < 30 then 1
      when callDuration > 600 then 12
      else floor(callDuration/60) + 2  end
   end as duration
  

• Use inline views to have a single source of the case

  select count(d.callid), d.duration
  from (   
     select callid
          , case
             when callDuration > 0 AND callDuration < 30 then 1
             when callDuration > 600 then 12
             else floor(callDuration/60) + 2  end
            end as duration
      from callmetatbl
      where programid = 1001
            and callDuration > 0
  ) d
  group by d.duration
  

• Or use common table expressions

     with duration_case as (
        select callid ,
        case
          when callDuration > 0 AND callDuration < 30 then 1
          when callDuration > 600 then 12
          else floor(callDuration/60) + 2  end
        end as duration
     from callmetatbl
     where programid = 1001 and callDuration > 0 )
      select count(callid), duration
      from duration_case
      group by duration
  

• Or use an user defined function (no example so far :-) )

• Or use a lookup table and a join

  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 >= t.durationFrom 
  AND callDuration < t.durationTo 
  where programid = 1001 and callDuration > 0
  

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).

Answer 1

Is there any reason you're not using between? The case statements themselves don't look too bad. If you really hate it you could throw all this into a table and map it.

Durations
------------------
low   high   value
0     30     1
31    60     2

etc...

(SELECT value FROM Durations WHERE callDuration BETWEEN low AND high) as Duration

EDIT: Or, in a case where floats are being used and between becomes cumbersome.

(SELECT value FROM Durations WHERE callDuration >= low AND callDuration <= high) as Duration

Answer 2

Divide callDuration by 60:

case
        when callDuration between 1 AND 29 then 1
        when callDuration > 600 then 12
        else (callDuration /60) + 2  end
end as duration

Note that between is inclusive of the bounds, and I'm assuming callDuration will be treated as an integer.

---

Update:
Combine this with some of the other answers, and you can get the entire query down to this:

select count(d.callid), d.duration
from (   
       select callid
            , case
                when callDuration between 1 AND 29 then 1
                when callDuration > 600 then 12
                else (callDuration /60) + 2  end
              end as duration
        from callmetatbl
        where programid = 1001
              and callDuration > 0
    ) d
group by d.duration

Answer 3

Q: how to get an alias to use in the GROUP BY clause

One approach is to use an inline view. [EDIT] The answer from Remus Rusanu (+1!) gives an example of a Common Table Expression to accomplish the same thing. [/EDIT]

The inline view gets you a simple "alias" for the complex expression which you can then reference in a GROUP BY clause in an outer query:

select count(d.callid)
     , d.duration
  from (select callid
             , case
               when callDuration >= 600 then 12
               when callDuration >= 540 then 11
               when callDuration >= 480 then 10
               when callDuration >= 420 then 9
               when callDuration >= 360 then 8
               when callDuration >= 300 then 7
               when callDuration >= 240 then 6
               when callDuration >= 180 then 5
               when callDuration >= 120 then 4
               when callDuration >=  60 then 3
               when callDuration >=  30 then 2
               when callDuration >    0 then 1
               --else null
               end as duration
             from callmetatbl
            where programid = 1001
              and callDuration > 0
       ) d
group by d.duration

Let's unpack that.

• the inner (indented) query is called and inline view (we given it an alias d)
• in the outer query, we can reference the alias duration from d

That should be sufficient to answer your question. If you're looking for an equivalent replacement expression, the one from tekBlues (+1 !) is the right answer (it works on the boundary and for non-integers.)

With the replacement expression from tekBlues (+1!):

select count(d.callid)
     , d.duration
  from (select callid
             , case 
               when callduration >=30 and callduration<600
                    then floor(callduration/60)+2
               when callduration>0 and callduration< 30
                    then 1 
               when callduration>=600
                    then 12
               end as duration
          from callmetatbl
         where programid = 1001
           and callDuration > 0
       ) d
 group by d.duration

(This should be sufficient to answer your question.)

---

[UPDATE:] sample user defined function (a replacement for inline CASE expression)

CREATE FUNCTION [dev].[udf_duration](@cd FLOAT)
RETURNS SMALLINT
AS
BEGIN
  DECLARE @bucket SMALLINT
  SET @bucket = 
  CASE
  WHEN @cd >= 600 THEN 12
  WHEN @cd >= 540 THEN 11
  WHEN @cd >= 480 THEN 10
  WHEN @cd >= 420 THEN 9
  WHEN @cd >= 360 THEN 8
  WHEN @cd >= 300 THEN 7
  WHEN @cd >= 240 THEN 6
  WHEN @cd >= 180 THEN 5
  WHEN @cd >= 120 THEN 4
  WHEN @cd >=  60 THEN 3
  WHEN @cd >=  30 THEN 2
  WHEN @cd >    0 THEN 1
  --ELSE NULL
  END
  RETURN @bucket
END

select count(callid)
     , [dev].[udf_duration](callDuration)
  from callmetatbl
 where programid = 1001
   and callDuration > 0
 group by [dev].[udf_duration](callDuration)

NOTES: be aware that the user defined function will add overhead, and (of course) add a dependency on another database object.

This example function is equivalent to the original expression. The OP CASE expression doesn't have any gaps, but it does reference each "breakpoint" twice, I prefer to test only the lower bound. (CASE returns when a condition is satisfied. Doing the tests in reverse lets the unhandled case (<=0 or NULL) fall through without test, an ELSE NULL is not necessary, but could be added for completeness.

ADDITIONAL DETAILS

(Be sure to check the performance and the optimizer plan, to make sure it's the same as (or not significantly worse than) the original. In the past, I've had problems getting predicates pushed into the inline view, doesn't look like it will be a problem in your case.)

stored view

Note that the inline view could also be stored as view definition in the database. But there's no reason to do that, other than to "hide" the complex expression from your statement.

simplifying the complex expression

Another way to make a complex expression "simpler" is to use a user defined function. But a user defined function comes with its own set of issues (including degraded performance.)

add database "lookup" table

Some answers recommend adding a "lookup" table to the database. I don't see that this is really necessary. It could be done of course, and could make sense if you want to be able to derive different values for duration from callDuration, on the fly, without having to modify your query and without having to run any DDL statements (e.g. to alter a view definition, or modify a user defined function).

With a join to a "lookup" table, one benefit is that you could make the query return different result sets by just performing DML operations on the "lookup" table.

But that same advantage may actually be a drawback as well.

Consider carefully if the benefit actually outweighs the downside. Consider the impact that new table will have on unit testing, how to verify the contents of the lookup table are valid and not changed (any overlaps? any gaps?), impact on ongoing maintenance to the code (due to the additional complexity).

some BIG assumptions

A lot of the answers given here seem to assume that callDuration is an INTEGER datatype. It seems they have overlooked the possibility that it's not an integer, but maybe I missed that nugget in the question.

It's fairly simple test case to demonstrate that:

callDuration BETWEEN 0 AND 30

is NOT equivalent to

callDuration > 0 AND callDuration < 30

Answer 4

the case can be written like this:

case 
when callduration >=30 and callduration<600 then floor(callduration/60)+2
when callduration>0 and callduration< 30 then 1 
when callduration>=600 then 12
end

The having is not needed, replace it by a "where callduration>0"

I like the translate table answer given before! that's the best solution

Answer 5

select count(callid), duration from
(
    select callid ,
    case
            when callDuration > 0 and callDuration < 30 then 1
            when callDuration >= 30 and callDuration < 60 then 2
            when callDuration >= 60 and callDuration < 120 then 3
            when callDuration >= 120 and callDuration < 180 then 4
            when callDuration >= 180 and callDuration < 240 then 5
            when callDuration >= 240 and callDuration < 300 then 6
            when callDuration >= 300 and callDuration < 360 then 7
            when callDuration >= 360 and callDuration < 420 then 8
            when callDuration >= 420 and callDuration < 480 then 9
            when callDuration >= 480 and callDuration < 540 then 10
            when callDuration >= 540 and callDuration < 600 then 11
            when callDuration >= 600 then 12
    end as duration
    from callmetatbl
    where programid = 1001 and callDuration > 0
) source
group by duration

Answer 6

Untested:

select  count(callid) , duracion
from
    (select 
     callid,
     case        
      when callDuration > 0 and callDuration < 30 then 1        
      when callDuration >= 30 and callDuration < 60 then 2        
      when callDuration >= 60 and callDuration < 120 then 3        
      when callDuration >= 120 and callDuration < 180 then 4        
      when callDuration >= 180 and callDuration < 240 then 5        
      when callDuration >= 240 and callDuration < 300 then 6        
      when callDuration >= 300 and callDuration < 360 then 7        
      when callDuration >= 360 and callDuration < 420 then 8        
      when callDuration >= 420 and callDuration < 480 then 9        
      when callDuration >= 480 and callDuration < 540 then 10        
      when callDuration >= 540 and callDuration < 600 then 11        
      when callDuration >= 600 then 12        
      else 0
     end as duracion
    from callmetatbl
    where programid = 1001) GRP
where duracion > 0
group by duracion

Answer 7

You need to push the CASE further down the query tree so that its projection is visible to the GROUP BY. This can be achieve in two ways:

1. Use a derived table (already Spencer, Adam and Jeremy showed how)

2. Use a common table expressions

   with duration_case as (
   select callid ,
   case
       when callDuration > 0 and callDuration < 30 then 1
       when callDuration >= 30 and callDuration < 60 then 2
       when callDuration >= 60 and callDuration < 120 then 3
       when callDuration >= 120 and callDuration < 180 then 4
       when callDuration >= 180 and callDuration < 240 then 5
       when callDuration >= 240 and callDuration < 300 then 6
       when callDuration >= 300 and callDuration < 360 then 7
       when callDuration >= 360 and callDuration < 420 then 8
       when callDuration >= 420 and callDuration < 480 then 9
       when callDuration >= 480 and callDuration < 540 then 10
       when callDuration >= 540 and callDuration < 600 then 11
       when callDuration >= 600 then 12
   end as duration
   from callmetatbl
   where programid = 1001 and callDuration > 0 )
      select count(callid), duration
      from duration_case
      group by duration
   

Both solutions are equivalent in every respect. I find CTEs more readable, some prefer derived tables as more portable.

Answer 8

Add all the cases into a table variable and do an outer join

DECLARE @t TABLE(durationFrom INT, durationTo INT, result INT)
--        when callDuration > 0 and callDuration < 30 then 1
INSERT INTO @t VALUES(1, 30, 1);
--        when callDuration >= 30 and callDuration < 60 then 2
INSERT INTO @t VALUES(30, 60, 2);

select count(callid) , COALESCE(t.result, 12)
from callmetatbl JOIN @t AS t ON callDuration >= t.durationFrom AND callDuration  < t.durationTo 
where programid = 1001 and callDuration > 0

Answer 9

Here's my shot at it. All of the components you need can be done in straight SQL.

select
  count(1) as total
 ,(fixedDuration / divisor) + adder as duration
from
(
    select
      case/*(30s_increments_else_60s)*/when(callDuration<60)then(120)else(60)end as divisor
     ,case/*(increment_by_1_else_2)*/when(callDuration<30)then(1)else(2)end as adder
     ,(/*duration_capped@600*/callDuration+600-ABS(callDuration-600))/2 as fixedDuration
     ,callDuration
    from 
      callmetatbl
    where
      programid = 1001
    and 
      callDuration > 0
) as foo
group by
  (fixedDuration / divisor) + adder

Here's the SQL I used for testing. (I don't have my own personal callmetatbl ;)

select
  count(1) as total
 ,(fixedDuration / divisor) + adder as duration
from
(
    select
      case/*(30s_increments_else_60s)*/when(callDuration<60)then(120)else(60)end as divisor
     ,case/*(increment_by_1_else_2)*/when(callDuration<30)then(1)else(2)end as adder
     ,(/*duration_capped@600*/callDuration+600-ABS(callDuration-600))/2 as fixedDuration
     ,callDuration
    from -- callmetatbl -- using test view below
      (  
       select 1001 as programid,   0 as callDuration union
       select 1001 as programid,   1 as callDuration union
       select 1001 as programid,  29 as callDuration union
       select 1001 as programid,  30 as callDuration union
       select 1001 as programid,  59 as callDuration union
       select 1001 as programid,  60 as callDuration union
       select 1001 as programid, 119 as callDuration union
       select 1001 as programid, 120 as callDuration union
       select 1001 as programid, 179 as callDuration union
       select 1001 as programid, 180 as callDuration union
       select 1001 as programid, 239 as callDuration union
       select 1001 as programid, 240 as callDuration union
       select 1001 as programid, 299 as callDuration union
       select 1001 as programid, 300 as callDuration union
       select 1001 as programid, 359 as callDuration union
       select 1001 as programid, 360 as callDuration union
       select 1001 as programid, 419 as callDuration union
       select 1001 as programid, 420 as callDuration union
       select 1001 as programid, 479 as callDuration union
       select 1001 as programid, 480 as callDuration union
       select 1001 as programid, 539 as callDuration union
       select 1001 as programid, 540 as callDuration union
       select 1001 as programid, 599 as callDuration union
       select 1001 as programid, 600 as callDuration union
       select 1001 as programid,1000 as callDuration
      ) as callmetatbl
    where
      programid = 1001
    and 
      callDuration > 0
) as foo
group by
  (fixedDuration / divisor) + adder

The SQL output is shown below, as 2 records counted for each duration (bucket) 1 through 12.

total  duration
2             1
2             2
2             3
2             4
2             5
2             6
2             7
2             8
2             9
2            10
2            11
2            12

Here are the results from the "foo" sub-query:

divisor adder   fixedDuration  callDuration
120         1               1             1
120         1              29            29
120         2              30            30
120         2              59            59
60          2              60            60
60          2             119           119
60          2             120           120
60          2             179           179
60          2             180           180
60          2             239           239
60          2             240           240
60          2             299           299
60          2             300           300
60          2             359           359
60          2             360           360
60          2             419           419
60          2             420           420
60          2             479           479
60          2             480           480
60          2             539           539
60          2             540           540
60          2             599           599
60          2             600           600
60          2             600          1000

Cheers.

Answer 10

What's so wrong with a User Defined Function here? You could both visually clean up the code and centralize the functionality that way. Performance-wise, I can't see the hit being too horrible unless you are doing something really retarded within said UDF.

Answer 11

Create a lookup table for duration
Using a look up table will speed up the SELECT statement as well.

Here is the end result of how it will look with lookup table.

select count(a.callid), b.ID as duration
from callmetatbl a
     inner join DurationMap b 
      on a.callDuration >= b.Minimum
     and a.callDuration < IsNUll(b.Maximum, a.CallDuration + 1)
group by  b.ID

Here is the look up table.

create table DurationMap (
 ID   int identity(1,1) primary key,
 Minimum  int not null,
 Maximum  int 
)

insert DurationMap(Minimum, Maximum) select 0,30
insert DurationMap(Minimum, Maximum) select 30,60
insert DurationMap(Minimum, Maximum) select 60,120
insert DurationMap(Minimum, Maximum) select 120,180
insert DurationMap(Minimum, Maximum) select 180,240
insert DurationMap(Minimum, Maximum) select 240,300
insert DurationMap(Minimum, Maximum) select 300,360
insert DurationMap(Minimum, Maximum) select 360,420
insert DurationMap(Minimum, Maximum) select 420,480
insert DurationMap(Minimum, Maximum) select 480,540
insert DurationMap(Minimum, Maximum) select 540,600
insert DurationMap(Minimum) select 600