WebOct 1, 2016 · 1 PRIMARY p1 ALL 407340 100.00 1 PRIMARY c1 ALL sp 412439 100.00 Using where; Using join buffer (Block Nested Loop) 2 UNION c1 ALL 412439 100.00 2 UNION p1 ref sp sp 1535 ccass.c1.stkcode,ccass.c1.participantname 70012 100.00 UNION RESULT ALL Using temporary WebAug 30, 2024 · 今天在写sql时,发现了一个慢sql,在测试环境上没问题,但是在正式环境查询非常缓慢。几张万级数据量的表关联操作,查询时间居然长达两分多钟。 查看执行计 …
mysql - Index is not used when joining two tables in a stored …
Web在这个过程里,对users表的全表扫描很耗时,对users表的每条数据跑到物化临时表里做全表扫描,很耗时,然后跟物化临时表做join,join的时候还要全表扫描物化临时表。 执行完上述SQL的EXPLAIN命令,看到执行计划后,可以执行一下show warnings命令。 WebOct 11, 2024 · MySQL executes joins between tables using a nested-loop algorithm or variations on it. Prior to MySQL 8.0.18, a Block Nested-Loop (BNL) join algorithm uses buffering of rows read in outer loops to reduce the number of times that tables in inner loops must be read algorithm was applied for equi-joins when no indexes could be used. – Terry … cheap cruises from messina
join表连接的三种算法思想:Nested-Loop Join和Index Nested-Loop Join和Block Nested …
WebApr 24, 2024 · mysql Using join buffer (Block Nested Loop) join连接查询优化. 更新,现在想想,查询效率不高,首先用explain分析查询语句,看看有没有用上索引,如果没有用上索 … WebApr 10, 2024 · Using index > NULL > Using where >= Using temporary > Using filesort 二、总结. MySQL执行计划的内容是SQL调优时的一个重要依据,我们想要优化SQL语句就必须得先掌握执行计划。这一篇主要是理论知识,也没什么好总结的。 总结一句话吧,想做MySQL调优,执行计划是必须要掌握的 ... WebA Block Nested-Loop (BNL) join algorithm uses buffering of rows read in outer loops to reduce the number of times that tables in inner loops must be read. For example, if 10 rows are read into a buffer and the buffer is passed to the next inner loop, each row read in the inner loop can be compared against all 10 rows in the buffer. cheap cruises from galveston tx