[英]How to optimze mysql subquery?
需要幫助來優化我的查詢,當前它運行大約22秒,並且該表中有110萬行。 這是我的查詢。 該查詢返回用戶的最新時間。
SELECT
t.id, t.user_id, t.created
FROM
timesheets t
WHERE
t.user_id IN (41649 , 41901,41899,41482,41648,41897,41652,
41483,41900,41143,41907,16,42191,42195,42194,42136,42193,42190,42484,42485,42486,42504,
42052,42797,42997,42868,42847,42505,42964)
AND t.id = (SELECT
MAX(sub_t.id)
FROM
timesheets AS sub_t
WHERE
sub_t.user_id = t.user_id
AND sub_t.description = 'in')
我也有該表的表索引(id,user_id,創建的,描述)。 任何建議都非常感謝。 謝謝
多列索引(user_id, id)
可能會有所幫助。
另外,也許使用聯接而不是相關子查詢。
SELECT
t.id, t.user_id, t.created
FROM
timesheets t
JOIN (
SELECT MAX(id) AS maxid
FROM timesheets t
WHERE user_id IN (41649 , 41901,41899,41482,41648,41897,41652,
41483,41900,41143,41907,16,42191,42195,42194,42136,42193,42190,42484,42485,42486,42504,
42052,42797,42997,42868,42847,42505,42964)
AND description = "in"
GROUP BY user_id) t1
ON t.id = t1.maxid
我假設id
是表的主鍵,所以它是唯一索引。
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