Return a rowset and set a variable in an "IN" clause in SQL Server - sql

Question

I want use the SQL Server IN operator and also set a variable to a column value. Is this possible?
My code is like this:
DECLARE #SubkindId as tinyint;
SELECT NAME FROM SampleTable001 WHERE
Id in (SELECT Id, #SubkindId = Subkind FROM SampleTable002)
ORDER BY Name;
My issue is: I want to set the #SubkindId variable in the inner select statement.

Answer 1

Can It Be Done?
In SQL Server you can't SELECT a result set and SET variables in the same statement (though you can in MySQL). Sorry. But there may be another way to get what you want. Unfortunately, what you want is not completely clear.
Assuming you want to do a SELECT and at the same time return another value into a variable, you have to handle the issue that your query can return multiple rows, so in that case, which one would you want to return into #SubkindId?
Now, I may have misunderstood, and instead of trying to pull the column value into the variable, you instead want to pull only the row where the SubkindId matches the value already in the variable (though you didn't show assigning a value to it first, so this seems less likely).
Please confirm which is the case and answer the above questions, and I can help you more.
In the meantime, I'll try to give you answers for both scenarios.
First, let me mention that I recommend against using the IN() syntax with a subquery returning a list of IDs. It is poor practice in my opinion because it usually demonstrates that the person doesn't really know how to JOIN properly, and as soon as the query gets a little complicated, not only that person but even the best professional SQL Server query writer can get lost (... WHERE x IN (SELECT ... WHERE y IN (SELECT ... WHERE z NOT IN (...))) which soon leads to a serious case of what!?!?!?!. Just use JOINs, and if required, semi-joins (introduced with an EXISTS clause).
Query and Return a Value
If what you really wanted was to get access to the values that the SELECT statement found while doing its join, it might look something like this:
DECLARE #KindsAndSubkinds TABLE (
Name varchar(100),
SubkindId tinyint
);
INSERT #KindsAndSubkinds
SELECT
T1.Name,
T2.SubkindId
FROM
dbo.SampleTable001 T1
INNER JOIN dbo.SampleTable002 T2
ON T1.Id = T2.Id
SELECT DISTINCT Name
FROM #KindsAndSubkinds
ORDER BY Name;
-- Now you can something with the `SubkindId`s in the #KindsAndSubkinds table variable.
Just Query
If you really were just trying to query rather than return a value, this is what I would recommend:
DECLARE #SubkindId as tinyint;
SET #SubkindId = 5;
SELECT
T1.Name
FROM
dbo.SampleTable001 T1
INNER JOIN dbo.SampleTable002 T2
ON T1.Id = T2.Id
WHERE
T2.Subkind = #SubkindId
ORDER BY
T1.Name;
If there are multiple rows in SampleTable002 but you don't want them in the result set, then:
SELECT
T1.Name
FROM
dbo.SampleTable001 T1
WHERE
EXISTS (
-- This semi-join requires at least one row to exist
-- but doesn't increase the row count
SELECT *
FROM dbo.SampleTable002 T2
WHERE
T1.Id = T2.Id
AND T2.Subkind = #SubkindId
)
ORDER BY
T1.Name;
I hope this helps.

Answer 2

Do it like this:
DECLARE #SubkindId as tinyint
SELECT [NAME]
FROM SampleTable001
WHERE Id in (SELECT Id
from SampleTable002
WHERE Subkind=#SubkindId)
order by [Name]
or by using JOIN
DECLARE #SubkindId as tinyint
SELECT [NAME]
FROM SampleTable001 a
INNER JOIN SampleTable002 b
ON a.id = b.id
WHERE b.Subkind=#SubkindId
order by [Name]