这种思想也应用到了软件中,MySQL中的innodb引擎也是以页为逻辑单位组织数据,只不过默认每页的大小是16kb,可以通过下面参数查看: mysql>select@@innodb_page_size,@@innodb_page_size/1024askb;+--------------------+---------+|@@innodb_page_size|kb|+--------------
慢查询日志是指 mysql中查询 时间超过固定阈值的查询记录,默认时间是10秒,mysql默认情况下不开启慢查询。 默认:show variables like "%slow_query_log%" 手动开启 set global 变量名 = 值。 set global slow_query_log =on ; 手动开启慢查询日志 set global long_query_time= 10; 手动设定查询时间超过的值,...
MySQL Indexes in MySQL are data structures that improve the speed of data retrieval operations on a database table. They are particularly useful in optimizing `JOIN` operations by reducing the amount of data MySQL needs to examine during query execution. ...
Re: Index for Query Posted by:Rick James Date: July 17, 2012 10:36PM SELECT SUM(b.`value`) AS cnt, COUNT(*) AS eCnt, a.`param6`, a.`cdate` AS timeline, COUNT(DISTINCT(a.`udid`)) AS userCnt FROM `event_logs` AS a JOIN `segment_users` AS c ON a.`udid` = c.`udid`...
MySQL can use the index to scan through people withzipcode='95054'. The second part (lastname LIKE '%etrunia%') cannot be used to limit the number of rows that must be scanned, so without Index Condition Pushdown, this query must retrieve full table rows for all people who havezipcode...
If you specify an index type that is not valid for a given storage engine, but another index type is available that the engine can use without affecting query results, the engine uses the available type. The parser recognizesRTREEas a type name, but currently this cannot be specified for ...
SUBSTRING_INDEX(str,delim,count) 语法格式说明 str:需要操作的字符串 delim:分隔符 count:匹配 delim 出现的次数,可正数可负数 栗子一 代码语言:javascript 代码运行次数:0 运行 AI代码解释 SELECTSUBSTRING_INDEX('www.mysql.com','.',1);# wwwSELECTSUBSTRING_INDEX('www.mysql.com','.',-1);# comSELEC...
Description: Simple "select" query gives wrong empty result depending on used index or even spacing between operators, and the only way to fix this - to run "analyze table". First time I got such behaviour on MySQL 5.6.27, then 28,29 and now on the current stable 5.7.11. Searching ...
首先来看,MySQL5.7和MySQL8.0中针对索引的排序语法。 00 MySQL5.7和MySQL8.0降序索引差异 MySQL5.7创建降序索引: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 mysql>create tabletest(c1 int,c2 int,indexidx_c1_c2(c1,c2 desc));QueryOK,0rowsaffected(0.01sec)mysql>show create table test\G***1....
I want to use the index on creation_date_time in the sub-query. However, explain plan shows that index on session_id is used (second line in the plan): +---+---+---+---+---+---+ | id | select_type | table | type | possible_keys | key | +---+---+---+---...