1
我跑这两个不同的查询,我不明白为什么在第一个销售表不使用索引为什么MySQL不使用索引
EXPLAIN SELECT COUNT(`sale`.`saleId`) AS `nb`
FROM `sale`
WHERE `sale`.`saleTransactionId` IN (
SELECT `transaction`.`transactionId`
FROM `transaction`
WHERE `transaction`.`transactionId` = 87587
)
结果是
result 1 http://snag.gy/SusqF.jpg
第二个
EXPLAIN SELECT COUNT(`sale`.`saleId`) AS `nb`
FROM `sale`
WHERE `sale`.`saleTransactionId` IN (87587)
结果是
result 2 http://snag.gy/ZgOXQ.jpg
中庸之道,以确保
SELECT `transaction`.`transactionId`
FROM `transaction`
WHERE `transaction`.`transactionId` = 87587
回报探微一行
saleTransactionId是INT(11)的transactionId 这两个表使用的MyISAM
销售指数结构
sale index structure http://snag.gy/we3HL.jpg
谢谢!