I\'m hoping there\'s a simple way to do this without using a sub-query:
Scenario: You have \"TableA\" with columns \"Key\", \"SubKey\", and \"Value\". I need to ge
SELECT MAX(Value)
FROM TableA t1
GROUP BY Key, SubKey
HAVING SubKey = (SELECT MAX(SubKey) FROM TableA t2 WHERE t1.Key = t2.Key)
AND Key = 1
Very simple, no join, no sub-query:
SELECT FIRST_VALUE(Value) OVER (ORDER BY SubKey DESC)
FROM TableA
WHERE Key = 1
If you need max value for each Key:
SELECT DISTINCT Key,
FIRST_VALUE(Value) OVER (PARTITION BY Key ORDER BY SubKey DESC)
FROM TableA
OMG Ponie's ROW_NUMBER
method is the one that will work best in all scenarios as it will not fail in the event of having two MAX
values with the same amount returning more records than expected and breaking a possible insert you might have being fed by that recordset
.
One thing that is missing is how to do it in the event of having to return the subkey associated to each max value, when there are also multiple keys. Simply join your summary
table with a MIN
and GROUP
"itself" and off you go.
WITH summary AS (
SELECT t.*,
ROW_NUMBER() OVER(ORDER BY t.subkey DESC) AS rank
FROM TABLE t
WHERE t.key = 1)
SELECT s.*
FROM summary s
join (select key, min(rank) as rank
from summary
group by key) sMAX
on s.key = sMAX.key and r.rank = sMAX.rank
OMG Ponies hit most of the ways to do it. Here's one more:
SELECT
T1.value
FROM
My_Table T1
LEFT OUTER JOIN My_Table T2 ON
T2.key = T1.key AND
T2.subkey > T1.subkey
WHERE
T2.key IS NULL
The only time that T2.key will be NULL is when there is no match in the LEFT JOIN, which means that no row exists with a higher subkey. This will return multiple rows if there are multiple rows with the same (highest) subkey.
If you'll always want just one row for one key value rather than the answer for many keys at once, all the join stuff is useless overbuilding. Just use the TOP 1 query OMG Ponies already gave you.
This will return all the values with subkey values that match, in case there are multiples.
SELECT a.value
FROM TABLE a
JOIN (SELECT MAX(t.subkey) AS max_subkey
FROM TABLE t
WHERE t.key = 1) b ON b.max_subkey = a.subkey
WHERE a.key = 1
This will return all the values with subkey values that match, in case there are multiples.
WITH summary AS (
SELECT t.*,
RANK() OVER(ORDER BY t.subkey DESC) AS rank
FROM TABLE t
WHERE t.key = 1)
SELECT s.value
FROM summary s
WHERE s.rank = 1
This will return one row, even if there are more than one with the same subkey value...
WITH summary AS (
SELECT t.*,
ROW_NUMBER() OVER(ORDER BY t.subkey DESC) AS rank
FROM TABLE t
WHERE t.key = 1)
SELECT s.value
FROM summary s
WHERE s.rank = 1
This will return one row, even if there are more than one with the same subkey value...
SELECT TOP 1
t.value
FROM TABLE t
WHERE t.key = 1
ORDER BY t.subkey DESC