EAV data in SQL Server - tsql

Question

I have no control over the data or the database structure. I have this EAV type of data where a consultant can speak one or many languages and he can travel to 1 or many countries in Europe and he has many skills indeed.
FYI there are 10 different main categories in my data.
Some consultants speak 10 languages while other speak only one.
The data looks a bit like this
____________________________________________
| ConsultantID | Category | Value |
--------------------------------------------
| 1 | Language | English |
| 1 | Language | French (fluent) |
| 1 | Language | Spanish (working)|
| 1 | Country | Ireland |
| 1 | Country | Italy |
| 1 | Country | Germany |
| 1 | Country | Belgium |
| 456 | Language | French (working) |
| 456 | Country | Belgium |
| 847 | Language | English |
| 847 | Country | Belgium |
--------------------------------------------
I want to list all consultants willing to travel to Belgium and who speak French (working or fluent). Based on my current example that would be #1 and #456
I wrote the query below which list all values matching a category for a consultant (note this is not dynamic as the number of value in my example is set to 5 max - so already a poor design).
SELECT
ID, category,
MAX(CASE seq WHEN 1 THEN value ELSE '' END ) +
MAX(CASE seq WHEN 2 THEN ',' + value ELSE '' END ) +
MAX(CASE seq WHEN 3 THEN ',' + value ELSE '' END ) +
MAX(CASE seq WHEN 4 THEN ',' + value ELSE '' END ) +
MAX(CASE seq WHEN 5 THEN ',' + value ELSE '' END )
FROM
(SELECT
p1.ID, p1.category, p1.value,
(SELECT COUNT(*)
FROM tblWebPracticeInfo p2
WHERE p2.category = p1.category
AND p2.ID = P1.ID
AND p2.value <= p1.value)
FROM
tblWebPracticeInfo p1) D (ID, category, value, seq )
GROUP BY
ID, category
ORDER BY
ID;
I would then need to query this table...
But without even a where clause it takes already 2 seconds to execute
I have something else more basic (but similarly not efficient)
select *
from tblWebMemberInfo m
where
m.ID in (select p.id from tblWebPracticeInfo p
where p.category = 'Language' and p.value like 'French%')
and m.ID in (select p.id from tblWebPracticeInfo p
where p.category = 'Country' and p.value = 'Belgium')
order by m.ID
That's basically where I am. As you can see nothing genius and nothing which is really working.
Can you point me to the right track.
I'm using SQL Server 2005 - v9.00.1
Many thanks in advance for your time & help

Answer 1

If you just need to list the consultants then you can use exists():
select p.Id ...
from Person p /* Assuming you have a regular table for people,
if not, use distinct or group by */
where exists (
select 1
from tblWebPracticeInfo l
where l.Id = p.Id
and l.Category = 'Language'
and l.Value = 'French'
)
and exists (
select 1
from tblWebPracticeInfo c
where c.Id = p.Id
and c.Category = 'Country'
and c.Value = 'Belgium'
)
You could also use aggregation and having like so:
select ConsultantID
from tblWebMemberInfo m
where (p.category = 'Language' and p.value like 'French%')
or (p.category = 'Country' and p.value = 'Belgium')
group by ConsultantID
having count(*) = 2 /* number of conditions to match is 2 */