[英]Faster select Max SQL Query
這是用於選擇具有最大行數的配置類型的查詢。 有沒有第二種查詢選擇數據一樣快的另一種方法呢?
select CONFIG_TYPE, MAX(COUNTING) FROM
(select CONFIG_TYPE, COUNT(*) as COUNTING FROM NOTIFICATION_CONFIG GROUP BY CONFIG_TYPE)
WHERE COUNTING =
(select MAX(COUNTING) FROM
(select COUNT(*) as COUNTING FROM NOTIFICATION_CONFIG GROUP BY CONFIG_TYPE)
)GROUP BY CONFIG_TYPE
第二個查詢將在1個搜索中完成工作,而另一個查詢將在2個搜索中完成工作。
select CONFIG_TYPE, COUNTING FROM
(select CONFIG_TYPE, COUNT(*) as COUNTING FROM NOTIFICATION_CONFIG
GROUP BY CONFIG_TYPE ORDER BY COUNTING DESC FETCH FIRST 1 ROW ONLY)
只是想知道是否還有另一種方法可以做到這一點。
使用窗口功能!
SELECT c.*
FROM (SELECT CONFIG_TYPE, COUNT(*) as COUNTING,
RANK() OVER (ORDER BY COUNT(*) DESC) as seqnum
FROM NOTIFICATION_CONFIG
GROUP BY CONFIG_TYPE
) c
WHERE seqnum = 1;
這使用RANK()
,因此它將返回所有最大值(在平局的情況下)。 如果要在ROW_NUMBER()
的情況下返回任意的最大值,請改用ROW_NUMBER()
。 或者,如果您不想要聯系,則可以執行以下操作:
SELECT CONFIG_TYPE, COUNT(*) as COUNTING
FROM NOTIFICATION_CONFIG
GROUP BY CONFIG_TYPE
ORDER BY COUNT(*) DESC
FETCH FIRST 1 ROW ONLY;
這只是搞砸了
select CONFIG_TYPE, MAX(COUNTING)
FROM ( select CONFIG_TYPE, COUNT(*) as COUNTING
FROM NOTIFICATION_CONFIG
GROUP BY CONFIG_TYPE
)
WHERE COUNTING = ( select MAX(COUNTING)
FROM ( select COUNT(*) as COUNTING
FROM NOTIFICATION_CONFIG
GROUP BY CONFIG_TYPE
)
)
GROUP BY CONFIG_TYPE
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