DEPENDENT typically signifies the use of a correlated subquery.DEPENDENT SUBQUERY evaluation differs from UNCACHEABLE SUBQUERY evaluation. For DEPENDENT SUBQUERY, the subquery is re-evaluated only once for each
如果等号两边的值、字符串或表达式都为字符串,则MySQL会按照字符串进行比较,其比较的 是每个字符串中字符的ANSI编码是否相等。 如果等号两边的值都是整数,则MySQL会按照整数来比较两个值的大小。 如果等号两边的值一个是整数,另一个是字符串,则MySQL会将字符串转化为数字进行比较。 如果等号两边的值、字符串或表达...
After the conversion, MySQL can use the pushed-down equality to limit the number of rows it must examine to evaluate the subquery. More generally, a comparison ofNvalues to a subquery that returnsN-value rows is subject to the same conversion. Ifoe_iandie_irepresent corresponding outer and ...
and the subquery returns either a single value as a result of a row set. Hence, the primary use of subquery can be to compute an instant value for another query to be executed.
分为simple(简单查询)、subquery(子查询)、drived(衍生表,from 列表中有子查询)、union(联合查询)等。 table 通常是表名,或者表的别名,或者一个为查询产生临时表的标示符(如派生表、子查询、集合)。 type 扫描类型(性能从高到低): null:MySQL在优化过程中分解语句,不需要访问索引或表就可以得到结果。
One thing that helps is to make sure you use a range variable on the subquery if there’s any columns in tables in the outer query that have the same name. I think what’s going on is mysql’s parser doesn’t do scoping very well and thinks the subquery may be correlated if there...
set_child() : opt_explain_json_namespace::context, opt_explain_json_namespace::subquery_ctx set_child_def_version() : Mrg_child_def set_child_schema_name() : dd::Foreign_key_parent set_child_table_name() : dd::Foreign_key_parent set_chunk() : Clone_Task_Manager set_class_origins(...
when nested queries were developed, which affects a large number of queries that use nested queries. There are plans to solve this problem, but scheduling is yet unknown. The only thing that you can try is to have an index on the column `Bol` and to avoid nested query by using prepared...
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)--关闭索引下推setoptimizer_switch='index_condition_pushdown=off';--开启索引下推setoptimizer_switch='index_condition_...
BROADCAST_SUBQUERY_ERROR schema=xxx process=xxx query_block=xxx message=xxx 小表广播模式查询的子查询失败,请检查SQL,或进一步联系技术支持。 30015 Select localnode by resource, all unavailable= NA 30016 CACHE_QUERY_FAILED message=xxx Cache表查询失败,请检查SQL,或进一步联系技术支持。 30017 COMPUTENODE执...