Stored procedure takes more than 30 seconds to execute - sql-server

Question

I am optimizing the stored procedure in which I get list of more than 10K user ids in one table variable as a parameter. I am setting flag #ContainsUserIds if there is any data into the table variable. In main query selecting the all the users that are present in table variable or all the users if no data found in table variable (There are more condition in where clause).
The problem is here that the statement in where clause takes more than 30 second which has OR condition. If I removed the first condition to check #ContainsUserIds = 0 then it will execute within a second. Can someone please help me to optimize this query.
This Stored procedure is called from different position so the User ids may not pass.
CREATE PROCEDURE [core].[spGetUsersByFilter]
(
#ClientId nvarchar(38) = NULL,
#UserIds [UserIdList] readonly
)
AS
BEGIN
SET NOCOUNT ON
DECLARE #ContainsUserIds BIT = 0,
SET #ContainsUserIds = CASE
WHEN EXISTS(SELECT TOP 1 1 FROM #UserIds)
THEN 1
ELSE 0
END;
SELECT DISTINCT ES.Id
FROM [db].[Users] E
JOIN [db].[UserDetails] ES ON ES.UserId = E.Id
WHERE E.[Active] = 1
AND (#ContainsUserIds = 0 OR E.UserId IN(SELECT Item FROM #UserIds))
AND ES.ClientId = #ClientId
END

Answer 1

SQL notoriously dislikes OR, the optimizer sometimes works around it but in most cases it's a good idea to convert things to a UNION [ALL] syntax. If there's just 1 OR that's often easy to do, if there are multiple things explode fast.
Anyway, you could thus convert your stored procedure to:
CREATE PROCEDURE [core].[spGetUsersByFilter]
(
#ClientId nvarchar(38) = NULL,
#UserIds [UserIdList] readonly
)
AS
BEGIN
SET NOCOUNT ON
DECLARE #ContainsUserIds BIT = 0,
SET #ContainsUserIds = CASE
WHEN EXISTS(SELECT * FROM #UserIds)
THEN 1
ELSE 0
END;
SELECT DISTINCT ES.Id
FROM [db].[Users] E
JOIN [db].[UserDetails] ES ON ES.UserId = E.Id
WHERE E.[Active] = 1
AND (#ContainsUserIds = 0)
AND ES.ClientId = #ClientId
UNION ALL
SELECT DISTINCT ES.Id
FROM [db].[Users] E
JOIN [db].[UserDetails] ES ON ES.UserId = E.Id
WHERE E.[Active] = 1
AND (#ContainsUserIds = 1)
AND E.UserId IN (SELECT Item FROM #UserIds))
AND ES.ClientId = #ClientId
END
That said, you might just as well split things up here and do 2 separate SELECTs. Also, if the table-variable contains more than a couple of records you may prefer to use a temp-table as the latter allows for indexing and most importantly has statistics handling which WILL result in a better execution plan. I also prefer JOIN over IN (), just make sure there are no doubled values when JOINing.
CREATE PROCEDURE [core].[spGetUsersByFilter]
(
#ClientId nvarchar(38) = NULL,
#UserIds [UserIdList] readonly
)
AS
BEGIN
SET NOCOUNT ON
SELECT DISTINCT Item
INTO #UserIds
FROM #UserIds
IF ##ROWCOUNT = 0
BEGIN
SELECT DISTINCT ES.Id
FROM [db].[Users] E
JOIN [db].[UserDetails] ES ON ES.UserId = E.Id
WHERE E.[Active] = 1
AND ES.ClientId = #ClientId;
END
ELSE
BEGIN
CREATE UNIQUE INDEX uq0_UserIds ON #UserIds ( Item ) WITH (FILLFACTOR = 100);
SELECT DISTINCT ES.Id
FROM [db].[Users] E
JOIN [db].[UserDetails] ES ON ES.UserId = E.Id
JOIN #UserIds T ON T.Item = E.UserId
WHERE E.[Active] = 1
AND ES.ClientId = #ClientId
END
END
PS: all above written in notepad and untested, some assembly may be required =)