这句话的意思是把查询语句的where都应用到表中返回的记录数最小的表开始查起,单表每个字段分别查询,看哪个字段的区分度最高2.explain查看执行计划,是否与1预期一致(从锁定记录较少的表开始查询)3.orderbylimit 形式的sql语句让排序的表优先查4.了解业务方使用场景5.加索引时参照建索引的几大原则6.观察结果,不...
#接着假定要取出userid为1的最近3次的购买记录,用的就是联合索引userid_2了,因为在这个索引中,在userid=1的情况下,buy_date都已经排序好了 mysql> explain select * from buy_log where userid=1 order by buy_date desc limit 3; +--+---+---+---+---+---+---+---+---+---+ |id|s...
1. 写出符合业务的SQL: select * from course where category_id=1and browse_times>1000 order by buy_times desc limit 1; 2.初步分析执行计划 2. 根据之前讲到的复合索引的概念, 以及在where条件和order by 排序中,需要建立复合索引 create index idx_cate_browse_buy oncourse(category_id,browse_times,b...
EXPLAIN FORMAT=TRADITIONAL FOR CONNECTION 'SELECT * FROM t1 UNION ALL SELECT * FROM t1 ORDER BY (SELECT * FROM t1 LIMIT 1)' id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t1 ALL NULL NULL NULL NULL 2 NULL 2 UNION NULL NULL NULL NULL NULL NULL NULL Pla...
ORDER BY path ); TODO: Operator ID is currently giving the physical operator ID as stored in the explain tables. It might be more appropriate to display a line number like the Oracle DBMS_XPLAN does so that it is more easy to find a specific ID. ...
You must "Buy" Scoring Edition to have unlimited access to these projects beyond the trial period 开始 [translate] atight with you 紧紧与您 [translate] aCompany enters the order demand information from each of its clients for Global Securities Offering into the Electronic Ticket Manager System ...
a3、工期目标 3rd, time limit for a project goal[translate] asome people feel satisfy when they buy something they like or pursue. 某些人感受满意当他们买事时他们喜欢或追求。[translate] aメッシュ Mesh[translate] a我希望这本书对你有用 I hoped this book is useful to you[translate] ...
“We have 34 everything very carefully,”said the officer 35 .“Our advance guards have drawn 36 of some forty thousand parts of the country for 37 by the spray teams.Each house in the malaria districts has been given a special 38 so that we can work in order.The United States has gi...
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Last week Friday was Ma Ruiya the birthday, her mother led her to buy the new skirt to the market.But Ma Ruiya does not want the new skirt.She takes 2 catties apples, her mother bought to her.She also wants some books and the water painter's brush, her mother also bought to her....