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.
#define ER_OUT_OF_RESOURCES 1041 "Out of memory; Check if mysqld or some other process uses all available memory. If not you may have to use 'ulimit' to allow mysqld to use more memory or you can add more swap space", #define ER_BAD_HOST_ERROR 1042 "Can't get hostname for you...
· 错误:1242 SQLSTATE: 21000 (ER_SUBQUERY_NO_1_ROW) 消息:子查询返回1行以上。 · 错误:1243 SQLSTATE: HY000 (ER_UNKNOWN_STMT_HANDLER) 消息:指定给%s的未知预处理语句句柄。 · 错误:1244 SQLSTATE: HY000 (ER_CORRUPT_HELP_DB) 消息:帮助数据库崩溃或不存在。 · 错误:1245 SQLSTATE: HY000 (ER...
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(...
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 ...
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_...
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。
Subquery is not grouped (explicitly or implicitly) 3x: outer aggregated expression are not accepted 4. Subquery does not use HAVING 5. Subquery does not use windowing functions 6. Subquery predicate is (a) in an ON/WHERE clause, and (b) at the AND-top-level of that clause. Note for ...
子查询(subquery)也叫嵌套查询 一个sql的结果会当成另外一个sql的条件 select * from sb where id = (select id from sb where id = 3); 将sql语句当表,写在from后面 将sql语句当条件,写在where后面-- 年龄大于学号为1001这个人的年龄 select age from stu where sid = 1001; select * from stu where...