Keep order from 'IN' clause

Question

Is it possible to keep order from a \'IN\' conditional clause?

I found this question on SO but in his example the OP have already a sorted \'IN\' clause.

My

Answer 1

There will be no reliable ordering unless you use an ORDER BY clause ..

SELECT SomeField,OtherField
FROM TestResult 
WHERE TestResult.SomeField IN (45,2,445,12,789)
order by case TestResult.SomeField
         when 45 then 1
         when 2  then 2
         when 445 then 3
         ...
         end

You could split the query into 5 queries union all'd together though ...

SELECT SomeField,OtherField
FROM TestResult 
WHERE TestResult.SomeField = 4
union all
SELECT SomeField,OtherField
FROM TestResult 
WHERE TestResult.SomeField = 2
union all
...

I'd trust the former method more, and it would probably perform much better.

Answer 2

There is an alternative that uses string functions:

with const as (select ',45,2,445,12,789,' as vals)
select tr.*
from TestResult tr cross join const
where instr(const.vals, ','||cast(tr.somefield as varchar(255))||',') > 0
order by instr(const.vals, ','||cast(tr.somefield as varchar(255))||',')

I offer this because you might find it easier to maintain a string of values rather than an intermediate table.

Answer 3

Try this:

SELECT T.SomeField,T.OtherField
FROM TestResult T
 JOIN 
   (
     SELECT 1 as Id, 45 as Val FROM dual UNION ALL
     SELECT 2, 2 FROM dual UNION ALL
     SELECT 3, 445 FROM dual UNION ALL
     SELECT 4, 12 FROM dual UNION ALL
     SELECT 5, 789  FROM dual
   ) I
   ON T.SomeField = I.Val
ORDER BY I.Id

Answer 4

Decode function comes handy in this case instead of case expressions:

SELECT SomeField,OtherField
FROM TestResult 
WHERE TestResult.SomeField IN (45,2,445,12,789)
ORDER BY DECODE(SomeField, 45,1, 2,2, 445,3, 12,4, 789,5)

Note that value,position pairs (e.g. 445,3) are kept together for readability reasons.

Answer 5

I was able to do this in my application using (using SQL Server 2016)

select ItemID, iName
  from Items
      where ItemID in (13,11,12,1)
      order by CHARINDEX(' ' + Convert("varchar",ItemID) + ' ',' 13 , 11 , 12 , 1 ')

I used a code-side regex to replace \b (word boundary) with a space. Something like...

var mylist = "13,11,12,1";
var spacedlist = replace(mylist,/\b/," ");

Importantly, because I can in my scenario, I cache the result until the next time the related items are updated, so that the query is only run at item creation/modification, rather than with each item viewing, helping to minimize any performance hit.