SQL Server. T-SQL. CASE IF EXISTS query - sql

Question

I have a classification table that looks like this:
ID CLASSIFICATION
__________________
A1 BOARD
A2 SURFBOARD
A3 SURF
Then I have a category table that looks like this
CATEGORY PARENT INDENT
____________________________________
SURF NULL 3
SURFBOARD SURF 2
BOARD SURFBOARD 1
I want to make a SQL query, that returns this:
INDENT3 INDENT2 INDENT1 ID
______________________________________
SURF NULL NULL A3
SURF SURFBOARD NULL A2
SURF SURFBOARD BOARD A1
Is it possible?. I'm not getting any ideas, seems like I need to loop through the classification table and find if there is indent1, indent2 and indent3. But not sure If I can put a script in a query, or if there is some kind of query I can do to achieve this. Something like
FOREACH CLASSIFICATION
CASE EXIST CATEGORY WITH IDENT1 INDENT 1 ELSE NULL AS IDENT1,
CASE EXIST CATEGORY WITH IDENT2 INDENT 2 ELSE NULL AS IDENT2,
CASE EXIST CATEGORY WITH IDENT1 INDENT 3 ELSE NULL AS IDENT3

Answer 1

If your hierarchy has a maximum of 3 levels a simpler query may be:
select cl.classification as indent3, null as indent2, null as indent1, id
from classification cl
join category ca on ca.category = cl.classification
where ca.indent = 3
union
select ca2.category, cl.classification, null as indent3, id
from classification cl
join category ca on ca.category = cl.classification
join category ca2 on ca.parent = ca2.category
where ca.indent = 2
union
select ca3.category as indent3, ca2.category as indent2, cl.classification as indent1, id
from classification cl
join category ca on ca.category = cl.classification
join category ca2 on ca.parent = ca2.category
join category ca3 on ca2.parent = ca3.category
where ca.indent = 1
If you have an indefinite number of parent/child levels you might be better to search "parent hierarchy with CTE" for a more complicated but flexible method.

Answer 2

Your logic is a bit hard to follow, but this should product the results that you specify:
select max(case when cl.indent = 3 then cl.category end) over () as indent3,
(case when cl.indent < 3
then max(case when cl.indent = 2 and then cl.category end) over ()
end) as indent2,
(case when cl.indent < 2
then max(case when cl.indent = 1 and then cl.category end) over ()
end) as indent1,
cl.id
from category ca join
classification cl
on ca.category = cl.category

Answer 3

People not so god with SQL will tell you to avoid this, SQL gurus consider to treat you as one of the pack.
It somewhat hard to understand your model but I gave it a shot.
Bit tip from the coach, if you need an id, use incremental numbers from the database, it's faster, allow god index and no risk of unexpected duplicates or truncation.
CREATE TABLE cs (id char(10), classification char(20));
CREATE TABLE ct (category char(20), parent char(20), indent int);
INSERT INTO cs VALUES
('A1','BOARD'),
('A2','SURFBOARD'),
('A3','SURF');
INSERT INTO ct VALUES
('SURF',null,3),
('SURFBOARD','SURF',2),
('BOARD','SURFBOARD',1);
select cs.id, ct1.category indent1,ct2.category indent2,ct3.category indent3 from ct ct1
left join ct ct2 on ct2.category = ct1.parent
left join ct ct3 on ct3.category = ct2.parent
left join cs on cs.classification = ct1.category
Link to the code on SQLFiddle