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[英]Select min of one column, max of another column and fields that go with max
[英]Select row based upon the MAX of one column and the related MIN of another
我有一個這樣的表:
CREATE TABLE dbo.IntervalCounts (
item_id int NOT NULL,
interval_time time(0) NOT NULL,
interval_count int DEFAULT 0 NOT NULL
)
每個item_id具有96個interval_time ,從00:00到23:45以15分鍾為增量。 每個interval_time的interval_count > = 0。 2億行。
我需要從計數最高的表中選擇值,然后,如果有多個具有相同計數的合格行,則選擇間隔時間最短的行。
因此,如果我有一個item_id 1,其最大計數為100:
item_id interval_time interval_count
1 00:00 100
1 13:15 100
1 07:45 100
1 19:30 100
我只想排一行:
item_id interval_time interval_count
1 00:00 100
獲得第一選擇很容易,我得到了:
SELECT a.item_id, a.interval_time, a.interval_count
FROM dbo.IntervalCounts a
LEFT JOIN dbo.IntervalCounts b
ON a.item_id = b.item_id
AND a.interval_count < b.interval_count
WHERE 1=1
AND b.interval_count IS NULL
但是,對我來說,將其降低到僅一排是很棘手的。
在我殺死它之前,這種三重自我連接運行了一個半小時(我將定期運行它,理想情況下,它最多運行不超過15分鍾)。
SELECT a.item_id, a.interval_time, a.interval_count
FROM dbo.IntervalCounts a
LEFT JOIN dbo.IntervalCounts b
ON a.item_id = b.item_id
AND a.interval_count < b.interval_count
LEFT JOIN dbo.IntervalCounts c
ON a.item_id = c.item_id
-- if I remove this line, it will ALWAYS give me the 00:00 interval
-- if I keep it, it runs way too long
AND a.interval_count = c.interval_count
AND a.interval_time > c.interval_time
WHERE 1=1
AND b.interval_count IS NULL
AND c.interval_time IS NULL
像這樣做起來似乎很費勁,而且我也被迫在大約一個半小時后終止執行:
DECLARE @tempTable TABLE
(
item_id int,
interval_time time(0),
interval_count int
)
INSERT INTO @tempTable
SELECT a.item_id, a.interval_time, a.interval_count
FROM dbo.IntervalCount a
LEFT JOIN dbo.IntervalCount b
ON a.item_id = b.item_id
AND a.interval_count < b.interval_count
WHERE 1=1
AND b.interval_count IS NULL
SELECT a.item_id, a.interval_time, a.interval_count
FROM @tempTable a
LEFT JOIN @tempTable b
ON a.item_id = b.item_id
AND a.interval_time > b.interval_time
WHERE 1=1
AND b.interval_time IS NULL
一定有更好的方法,但是我很沮喪。 如何以一種不會永遠運行的方式來做到這一點?
您想得太多了,可以使用ROW_NUMBER
:
WITH CTE AS
(
SELECT *,
RN = ROW_NUMBER() OVER(PARTITION BY item_id
ORDER BY interval_count DESC, interval_time)
FROM dbo.IntervalCounts
)
SELECT *
FROM CTE
WHERE RN = 1;
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