Semi-Tricky SQL Query - sql

Question

I am trying to write a query for SQL Server 2005 but I can't figure out how to do it. I have a table with the following fields:
MessageID int
CategoryID int
Priority tinyint
MessageText NVARCHAR(MAX)
I need a query that will return * for each row that has the highest priority within a Category. For example, if I had the following data:
MessageID, CategoryID, Priority, MessageText
1, 100, 1, Error #1234 occurred
2, 100, 2, Error #243 occurred
3, 100, 3, Error #976 occurred
4, 200, 4, Error #194 occurred
5, 200, 1, Error #736 occurred
6, 300, 3, Error #54 occurred
7, 300, 2, Error #888 occurred
then the result would be:
MessageID, CategoryID, Priority, MessageText
3, 100, 3, Error #976 occurred
4, 200, 4, Error #194 occurred
6, 300, 3, Error #54 occurred
Notice that it returns one row per category, and that it is the row which had the highest priority for that Category.
Can anyone tell me how I can write this query?

Answer 1

Verified:
SELECT
highest_priority_messages.*
FROM
(
SELECT
m.MessageID
, m.CategoryID
, m.Priority
, m.MessageText
, Rank() OVER
(PARTITION BY m.CategoryID ORDER BY m.Priority DESC) AS p_rank
FROM [Message] m
GROUP BY
m.CategoryID
, m.Priority
, m.MessageID
, m.MessageText
) highest_priority_messages
WHERE
p_rank = 1

Answer 2

I believe that this should work, table name assumed as Messages
SELECT
M.MessageId,
M.CategoryId,
M.Priority,
M.MessageText
FROM
(
SELECT
CategoryId,
MAX(Priority) AS Priority
FROM Messages
GROUP BY CategoryId
) AS MaxValues
INNER JOIN Messages M
ON (MaxValues.CategoryId = M.CategoryId
AND MaxValues.Priority = M.Priority)
NOTE
The only "gotcha" in this method is that if you have more than one max priority...

Answer 3

If you'd like to do it without all of the subqueries:
SELECT
MessageID,
CategoryID,
Priority,
MessageText
FROM
dbo.Messages M1
LEFT OUTER JOIN dbo.Messages M2 ON
M2.CategoryID = M1.CategoryID AND
M2.Priority > M1.Priority
WHERE
M2.MessageID IS NULL
You might have to adjust the query depending on how you want to handle ties. You didn't have any such examples, so I wasn't sure.

Answer 4

select distinct query1.* from
(select categoryId,msgText,max(priorityId) as MAX_PRIORITY
from message
group by categoryId,msgText
order by categoryId
) query1,
(select categoryId,max(priorityId) as MAX_PRIORITY
from message
group by categoryId
order by categoryId
) query2
where query1.MAX_PRIORITY = query2.MAX_PRIORITY
order by query1.categoryId

Answer 5

SELECT
Messages.MessageID
, Messages.CategoryID
, Messages.Priority
, Messages. MessageText
FROM
Messages
INNER JOIN
(
SELECT
CategoryID
, MAX(Priority) AS Priority
FROM
Messages
GROUP BY
CategoryID
) AS MaxResults
ON
(
Messages.CategoryID = MaxResults.CategoryID
AND
Messages.Priority = MaxResults.Priority
)
It looks like this is basically the same answer given above... with the same Caveat.
Although this one will work right off the bat.

Answer 6

This is shorter and easier to read (imo).
select ms.*
from
messages ms
,(
select ms1.categoryid, max(ms1.priority) as max_priority
from messages ms1
group by ms1.categoryid
) tmp
where ms.categoryid = tmp.categoryid
and ms.priority = tmp.max_priority;

Answer 7

SELECT DISTINCT CategoryId,PS.Priority,MessageID,MessageText
FROM Priority_Scene PS
JOIN (SELECT MAX(Priority) AS Priority FROM Priority_Scene GROUP BY CategoryId) A
ON A.Priority = PS.Priority

Answer 8

I'm not quite high enough rank (yet) to post a comment, so I'd like to add to cfeduke's solution:
SELECT
highest_priority_messages.*
FROM
(
SELECT
m.MessageID
, m.CategoryID
, m.Priority
, m.MessageText
, Rank() OVER
(PARTITION BY m.CategoryID ORDER BY m.Priority DESC, m.MessageID DESC) AS p_rank
FROM [Message] m
GROUP BY
m.CategoryID
, m.Priority
, m.MessageID
, m.MessageText
) highest_priority_messages
WHERE
p_rank = 1
If you add another CategoryID 100 Message with Priority 3, the original solution would bring back 2 rows, by adding another order condition we eliminate the chance of two items ranking the same.
Here's a copy of the row I inserted to test this.
insert into [Message] (MessageID, CategoryID, Priority, MessageText)
select 8, 100, 3, 'Error #976-2 occurred'