VLOOKUP-style range lookup in T-SQL - sql-server

Question

Here's a tricky problem I haven't quite been able to get my head around. I'm using SQL Server 2008, and I have a sparse range table that looks like this:
Range Profession
----- ----------
0 Office Worker
23 Construction
54 Medical
Then I have another table with values that are within these ranges. I'd like to construct a query which joins these two tables and gives me the Profession value that is less than or equal to the given value. So let's say my other table looks like this:
Value
29
1
60
Then I'd like my join to return:
Value Profession
----- ----------
29 Construction
1 Office Worker
60 Medical
(because 29>the 23 for Construction but <=the 54 for Medical)
Is there any way I can get SQL to bend to my will in this manner, short of actually blowing out the range table to include every possible value?
Thank you.

Answer 1

Easist Way to do this is to add a another column to you sparse range table.
LowRange HighRange Profession
0 22 Office Worker
23 53 Construction
54 999999 Medical
Then use a query like this to get the range(table 2 is the one with the 29,1,60 values):
SELECT Table_2.JoinKey as Value, Table_1.Description as Profession
FROM Table_1 INNER JOIN Table_2
ON Table_2.JoinKey => Table_1.LowRangeKey
AND Table_2.JoinKey <= Table_1.HighRangeKey;

Answer 2

You could use CROSS APPLY:
select v.Value, p.Profession
from tblValues v
cross apply
(select top(1) pr.Profession
from tblProfessionRanges pr
where pr.Range <= v.Value ORDER BY pr.[Range] DESC) p
It should be faster than using max and doesn't need a max-range do be maintained.

Answer 3

I think I understand your problem. I created a table called professions with your values and a map_vals table with the look up values. Then I came up with this:
select p.range as `range1`, p.profession, v.value from professions p
inner join map_vals v ON v.value >= p.range
where p.range =
(select max(p3.range) from professions p3 where p3.range <= v.value)
order by v.value
which when given these values...
value
29
0
60
1
23
54
returns
range1 profession value
0 Office Worker 0
0 Office Worker 1
23 Construction 23
23 Construction 29
54 Medical 54
54 Medical 60
EDIT:
You could also use CROSS APPLY as shown by manfred-sorg but it requires an ORDER BY DESC or you will get the following:
select v.Value, p.Profession
from tblValues v
cross apply
(select top(1) pr.Profession
from tblProfessionRanges pr
where pr.Range <= v.Value) p
produces
Value Profession
----------- --------------------------------------------------
29 Office Worker
1 Office Worker
60 Office Worker
to get your desired result you need to change it to:
select v.Value, p.Profession
from tblValues v
cross apply
(select top(1) pr.Profession
from tblProfessionRanges pr
where pr.Range <= v.Value ORDER BY pr.[Range] DESC) p
Value Profession
----------- --------------------------------------------------
29 Construction
1 Office Worker
60 Medical
However, the sorting required here makes it less efficient than using MAX.