unique_subquery is just an index lookup function that replaces the subquery completely for better efficiency. unique_subquery是一个索引查找函数,代替子查询提高效率。 index_subquery This join type is similar to unique_subquery.
merges two record sets by looping through every record in the first set and trying to find a match in the second set. All matching records are returned. 遍历模式 索引模式 5、聚合 - Aggregate group by 操作 groups records together based on a GROUP BY or aggregate function (like sum()). 6...
│ Function equals (children 1) │ │ ExpressionList (children 2) │ │ Identifier t1.UserID │ │ Identifier t2.UserID │ └────────────────────────────────────────────────────┘ 44 rows in set. Elapsed: 0.001 sec. 1. ...
unique_subquery 在IN子查询时用于替换ref类型,例如 valueIN(SELECTprimary_keyFROMsingle_tableWHEREsome_expr) unique_subquery是一个索引查找函数,用于替换子查询,已达到更高的效率。 index_subquery 和unique_subquery类似,用于替换IN的子查询,但它用于对那些非unique的index的子查询,例如 valueIN(SELECTkey_columnFROM...
首先要确保相信函数的变量log_bin_trust_function_creators为1 存储过程 向s1、s2表添加数据的存储过程 执行存储过程添加数据 Explain的输出列 列名 描述 id 在一个大的查询语句中每个SELECT关键字都对应着一个唯一的id select_type SELECT关键字对应查询的类型 ...
log_bin_trust_function_creators为1 SELECT @@log_bin_trust_function_creators variable; SET GLOBAL log_bin_trust_function_creators = 1; 存储过程 向s1、s2表添加数据的存储过程 DELIMITER // CREATE PROCEDURE insert_s1 (IN min_num INT (10), IN max_num INT(10)) BEGIN DECLARE i INT ...
2CREATE DEFINER=`root`@`localhost` FUNCTION `generateDateTime`(begin_time char(10), end_time char(10)) RETURNS datetime 3BEGIN 4 #Routine body goes here... 5 DECLARE date_time VARCHAR ( 255 ) DEFAULT ''; 6 DECLARE local_date VARCHAR ( 255 ) DEFAULT ''; ...
The refcolumnshows which columnsorconstants are comparedtotheindexnamedinthekeycolumntoselectrowsfromthetable.Ifthe valueisfunc, the value usedisthe resultofsomefunction.Tosee whichfunction,useSHOW WARNINGS following EXPLAINto see the extended EXPLAIN output. Thefunctionmight actually be an operator such...
valueIN(SELECTprimary_keyFROMsingle_tableWHEREsome_expr) unique_subquery is just an index lookup function that replaces the subquery completely for better efficiency. unique_subquery是一个索引查找函数,代替子查询提高效率。 index_subquery This join type is similar to unique_subquery. It replaces IN ...
--->Block_ops_in:阻塞的输入操作 --->Block_ops_out:阻塞的输出操作 --->Messages_sent:消息发出 --->Messages_received:消息接受 --->Page_faults_major:主分页错误 --->Page_faults_minor:次分页错误 --->Swaps:交换次数 --->Source_function:源功能 --->Source_...