`hire_date` dateNOTNULL,PRIMARYKEY(`emp_no`),KEY`idx_first_last` (`first_name`,`last_name`) USING BTREE ) ENGINE=InnoDBDEFAULTCHARSET=utf8; mysql>explainselect*fromemployeeswherefirst_name='Tomofumi'andlast_name='Asmuth';+---+---+---+---+---+---+---+---+---+---+|id|se...
PRIMARY 和 SUBQUERY 执行sql如下： explain select * from test1 t1 where t1.id = (select id from...
该查询使用 PRIMARY索引来执行查询，从rows列可以看出满足id > 5890的记录有5286条。
const用于用常数值比较PRIMARY KEY或UNIQUE索引的所有部分时。在下面的查询中,tbl_name可以用于const表:1 2 3 4 SELECT * FROM tbl_name WHERE primary_key=1; SELECT * FROM tbl_name WHERE primary_key_part1=1 AND primary_key_part2=2; 例如: 1 2 3 4 5 6 7 mysql> explain select * from ...
For InnoDB, a secondary index might coverthe selected columns even if the query also selects the primary key becauseInnoDB stores the primary key value with each secondary index. If key is NULL,MySQL found no index to use for executing the query more efficiently. ...
It is a collection of storage cells together with associated circuits needed to transfer information in and out of storage. There are two types of computer memory: Primary memory and secondary memory. RAM and ROM are termed as primary memory. Hard disk, floppy disk, ...
For InnoDB, a secondary index might coverthe selected columns even if the query also selects the primary key becauseInnoDB stores the primary key value with each secondary index. If key is NULL,MySQL found no index to use for executing the query more efficiently. ...
The processes of primary and secondary succession in an extremely long period time period? True or false? Explain.Succession:In biology and ecology, succession refers to processes in which plants or other species take on different structures. This can result in ...
Batteries come in all different shapes, sizes, voltages, and capacities (amounts of stored charge or energy). Although they can be made with all sorts of different chemical electrolytes and electrodes, there are really only two main types: primary and secondary.Primary batteriesare ordinary, dispo...
Other than the system and const types, this is the best possible join type. It is used when all parts of an index are used by the join and the index is a PRIMARY KEY or UNIQUE NOT NULL index. eq_ref can be used for indexed columns that are compared using the = operator. The ...