conditional where clause - sql

Question

I need filter result of a join query between two tables but I don't have a condition for the "where clause".
What I need is to filter based on id_project like this:
if id_project is equal to 24 (24 is the default project) then it should return only rows with
id_project =24. here rows 1,3...10 will be selected
if id_project is equal to 25, then I need those rows which have id_project=25 plus those rows which has " id_project=24 and not id_project 25, so rows number 2 to 11 will be selected
With this query :
SELECT tp.id_tag, tp.id_project, tp.NJTagName, tp.node_level , tl.id_level
FROM instrumentation.dbo.tag_project tp
INNER JOIN instrumentation.dbo.tag_level tl
ON tl.id_tag=tp.id_tag
//
where tl.id_level=69 and tp.node_level=1
I get this result :
How can I change my query to do this?

Answer 1

Thinking a little more about your request, it burns down to: For every id_tag give me the ID requested, or 24 if not available. This can be done in one query, where you use a ranking with ROW_NUMBER, in which you prefer the requested ID over the 24.
select *
from
(
select
tp.*,
row_number() over(partition by id_tag
order by case when id_project = 24 then 2 else 1 end) as rn
from tag_project tp
where id_project in (24, #REQUESTED_ID)
) ranked
where rn = 1;
Here is your original query changed accordingly:
SELECT id_tag, id_project, NJTagName, node_level, id_level
FROM
(
SELECT tp.id_tag, tp.id_project, tp.NJTagName, tp.node_level , tl.id_level
, row_number() over (partition by tp.id_tag order by case when tp.id_project = 24 then 2 else 1 end) as rn
FROM instrumentation.dbo.tag_project tp
INNER JOIN instrumentation.dbo.tag_level tl ON tl.id_tag=tp.id_tag
WHERE tl.id_level=69 AND tp.node_level=1
AND tp.id_project in (24, #REQUESTED_ID)
) ranked
WHERE rn = 1;

Answer 2

So depending of whether the user asks for ID 24 or not there are two different queries to execute.
Here is the query for ID 24:
select *
from tag_project
where id_project = 24;
Here is the query for #OTHERID. We use UNION ALL to combine the 24 records with the #OTHER records. And we use NOT EXISTS in order to avoid certain records.
select *
from tag_project
where id_project = #OTHERID
union all
select *
from tag_project tp
where id_project = 24
and not exists
(
select *
from tag_project tp2
where tp2.id_tag = tp.id_tag
and tp2.id_project = #OTHERID
);

Answer 3

You can write like this for default case pass #otherId as NULL.
SELECT tp.id_tag, tp.id_project, tp.NJTagName, tp.node_level , tl.id_level
FROM instrumentation.dbo.tag_project tp
INNER JOIN instrumentation.dbo.tag_level tl
ON tl.id_tag=tp.id_tag
where tl.id_level=69 and tp.node_level=1 AND tp.id_project = ISnull(#otherId, 24)

Answer 4

Use in:
SELECT tp.id_tag, tp.id_project, tp.NJTagName, tp.node_level , tl.id_level
FROM instrumentation.dbo.tag_project tp
INNER JOIN instrumentation.dbo.tag_level tl
ON tl.id_tag=tp.id_tag
//
where tl.id_level=69 and tp.node_level=1
and tp.id_project in (24, #OTHERID)
UPDATE:
If you want only one id_project instead, use can also use aggregation method.
SELECT tp.id_tag, tp.NJTagName, tp.node_level , tl.id_level
case when count(distinct tp.id_project) = 2 then #OTHERID
else 24 end as id_project
FROM instrumentation.dbo.tag_project tp
INNER JOIN instrumentation.dbo.tag_level tl
ON tl.id_tag=tp.id_tag
WHERE tl.id_level=69 and tp.node_level=1
AND tp.id_project in (24, #OTHERID)
GROUP BY tp.id_tag, tp.NJTagName, tp.node_level , tl.id_level