classCondition_pushdown{public:boolmake_cond_for_derived();Item*make_remainder_cond(Item*cond);Item*get_remainder_cond(){returnm_remainder_cond;}private:/// Condition that needs to be checked to push down to the derived table.Item*m_cond_to_check;/// Derived table to push the condition t...
When a derived table cannot be merged into the outer query (for example, if the derived table uses aggregation), pushing the outer WHERE condition down to the derived table should decrease the number of rows that need to be processed and thus speed up execution of the query. 也就是说合并...
Mysql 8.0.22之后的版本支持派生条件回移(Derived Condition Pushdown)优化。该优化可以减少派生表处理的行数从而提高查询执行的效率。比方说有如下查询: SELECT * FROM (SELECT i, j FROM t1) AS dt WHERE i > constant 1. 2. 3. 通过派生条件回移优化后类似如下形式(WHERE条件拿到派生表的里面): SELECT *...
SHOWVARIABLESLIKE'derived_condition_pushdown'; 1. 该命令将返回当前的derived_condition_pushdown设置值。 2. 设置 derived_condition_pushdown 为 OFF 要将derived_condition_pushdown设置为OFF,我们可以使用以下 SQL 命令: SETGLOBALderived_condition_pushdown=OFF; 1. 请注意,设置 GLOBAL 可能需要管理员权限,并且更...
这个语句最大的特点就是运用了派生表(derived table),MySQL在8.0.22版本上引入了一个关于派生表的优化器开关derived_condition_pushdown, 默认设置为on。我们看一下关于这个特性在官方文档中的描述: MySQL 8.0.22 and later supports derived condition pushdown for eligible subqueries. For a query such as SELECT...
这个语句最大的特点就是运用了派生表(derived table),MySQL在8.0.22版本上引入了一个关于派生表的优化器开关derived_condition_pushdown, 默认设置为on。我们看一下关于这个特性在官方文档中的描述: MySQL 8.0.22 and later supports derived condition pushdown for eligible subqueries. For a query such as SELECT...
Version:8.1.0, 8.0.34OS:Ubuntu (22.04) Assigned to:CPU Architecture:x86 (x86_64) Tags:Derived condition push down [30 Jul 2023 5:35] Pedro Ferreira Description:Run these queries: SET SESSION optimizer_switch='derived_condition_pushdown=on'; SELECT 1 FROM (SELECT b'1') y(y) WHERE (NUL...
这个语句最大的特点就是运用了派生表(derived table),MySQL在8.0.22版本上引入了一个关于派生表的优化器开关derived_condition_pushdown, 默认设置为on。我们看一下关于这个特性在官方文档中的描述: MySQL 8.0.22 and later supports derived condition pushdown for eligible subqueries. For a query such as SELECT...
MySQL8.0.22~MySQL8.0.25 因为优化器新特性derived_condition_pushdown带来的bug,可以通过derived merge与derived_condition_pushdown 的使用限制以及优化器开关hint来有效规避bug,当然升级到高版本更好。 如果想让新特性derived_condition_pushdown发挥作用,就要避开它的使...
key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on1rowinset (0.00sec)切换状态：set="index_condition_pushdown=off";set="index_condition_pushdown=on";