Improve SQL query performance. UNION vs OR in this situation - sql

Question

Problem
So the situation that I am facing here with this SQL Query, is that it is taking about 12 seconds to run making the screen super slow.
Goal
Do the necessary changes in order to improve the performance and make it faster. I was thinking about instead of the OR in the Where clause to use the UNION?
SELECT Tool.*, Interview.*
FROM Tool
INNER JOIN Interview ON Interview.Id = Tool.InterviewId
WHERE (Tool.ToolTypeId = #ToolTypeId
AND Tool.Is_Active = 1
AND Tool.InterviewId = #InterviewId
AND Tool.ToolId = #ToolId
AND Tool.CustomerId = #CustomerId)
OR Tool.Id = (
SELECT TOP 1 SubTool.Id
FROM Tool SubTool
INNER JOIN Interview subInterview ON subInterview.Id = SubTool.ToolId
WHERE SubTool.ToolTypeId = #ToolTypeId
AND SubTool.Is_Active = 1
AND SubTool.InterviewId != #InterviewId
AND SubTool.ToolId = #ToolId
AND subTool.CustomerId = #CustomerId
AND convert(datetime, subTool.DateTime, 120) < #ToolDateTime
ORDER BY subTool.DateTime DESC, subTool.StartDate DESC,
subTool.EndDate, subTool.Id DESC
)
ORDER BY Tool.StartDate, Tool.Id
NOTE: I believe the actual query output is not necessary in this case, since we are looking for some structural issues that might be impacting the performance.

Answer 1

I would suggest rephrasing the query to eliminate the subquery in the WHERE clause.
If you are looking for one row in the result set regardless of conditions, you can use:
SELECT TOP (1) Tool.*, Interview.*
FROM Tool JOIN
Interview
ON Interview.Id = Tool.InterviewId
WHERE Tool.ToolTypeId = #ToolTypeId AND
Tool.Is_Active = 1
Tool.ToolId = #ToolId AND
Tool.CustomerId = #CustomerId AND
(Tool.InterviewId = #InterviewId OR
convert(datetime, Tool.DateTime, 120) < #ToolDateTime
)
ORDER BY (CASE WHEN Tool.InterviewId = #InterviewId THEN 1 ELSE 2 END),
Tool.DateTime DESC, sTool.StartDate DESC, Tool.EndDate, Tool.Id DESC;
Your final ORDER BY suggests that you are expecting more than one row for the first condition. So, you can use a subquery and window functions:
SELECT ti.*
FROM (SELECT Tool.*, Interview.*,
COUNT(*) OVER (PARTITION BY (CASE WHEN Tool.InterviewId = #InterviewId THEN 1 ELSE 0 END)) as cnt_interview_match,
ROW_NUMBER() OVER (ORDER BY subTool.DateTime DESC, subTool.StartDate DESC, subTool.EndDate, subTool.Id DESC) as seqnum
FROM Tool JOIN
Interview
ON Interview.Id = Tool.InterviewId
WHERE Tool.ToolTypeId = #ToolTypeId AND
Tool.Is_Active = 1
Tool.ToolId = #ToolId AND
Tool.CustomerId = #CustomerId AND
(Tool.InterviewId = #InterviewId OR
convert(datetime, Tool.DateTime, 120) < #ToolDateTime
)
) ti
WHERE InterviewId = #InterviewId OR
(cnt_interview_match = 0 AND seqnum = 1);
Note that the subquery requires that the columns have different names, so you might need to fiddle with that.
Then, you want an index on TOOL(ToolTypeId, Is_Active, ToolId, CustomerId, InterviewId, DateTime). I assume that Interview(Id) is already indexed as the primary key of the table.

Answer 2

My interpretation of what your query does (and by inference, what you want it to do) is different from #GordonLinoff's.
Gordon's queries could be paraphrased as...
If there are rows with Tool.InterviewId = #InterviewId...
Return those rows and only those rows
If there are no such rows to return...
Return the latest row for other InterviewId's
My understanding of what your query actually does is that you want both possibilities returned together, at all times.
This ambiguity is an example of why you really should include example data.
For example, this would be a re-wording or your existing query (using UNION as per your own suggestion)...
WITH
filter_tool_customer AS
(
SELECT Tool.*, Interview.*
FROM Tool
INNER JOIN Interview ON Interview.Id = Tool.InterviewId
WHERE Tool.ToolTypeId = #ToolTypeId
AND Tool.Is_Active = 1
AND Tool.ToolId = #ToolId
AND Tool.CustomerId = #CustomerId
),
matched AS
(
SELECT *
FROM filter_tool_customer
WHERE InterviewId = #InterviewId
),
mismatched AS
(
SELECT TOP 1 *
FROM filter_tool_customer
WHERE InterviewId <> #InterviewId
AND DateTime < CONVERT(VARCHAR(20), #ToolDateTime, 120)
ORDER BY DateTime DESC,
StartDate DESC,
EndDate,
Id DESC
),
combined AS
(
SELECT * FROM matched
UNION ALL
SELECT * FROM mismatched
)
SELECT * FROM combined ORDER BY StartDate, Id