How does MySQL create, delete, and view indexes?

mysql It is an open source database with a wide range of applications .mysql The index inside can use pointers , Can greatly improve the query efficiency . Especially when the amount of data is very large , When a query involves multiple tables , Using indexes can often speed up queries thousands of times . that , How to create an index ？

1. First step , Create a table , The structure is as follows ：create table t (id int unsigned not null,name varchar(20) not null default ‘-‘);

1. The second step , Add index , Second, the index is divided into several categories , General index , primary key , And unique index , The steps are shown in the figure ： Number in the figure 123 It corresponds to the general index , primary key , And unique index alter table Table name add index/unique/primary key ( Index name );

1. The third step , There is already an index in the table , How to check ？ With these two commands ：show index from table; or show keys from table; Pictured ： show index from Table name ; show keys from Table name ;

1. Step four , Sometimes there are too many indexes , It will cause the performance of adding, deleting, modifying and checking , So you can create it and delete it , The order is as follows ： drop index Index name on Table name ; DROP INDEX index_name ON talbe_name; ALTER TABLE table_name DROP INDEX index_name; ALTER TABLE table_name DROP PRIMARY KEY;

1. Step five , When deleting the index above , There was a mistake , Say that the index name cannot be found , Because it was deleted the first time , therefore , This index name no longer exists , Pictured

1. Step six , Query the index again , Whether the deletion was successful , Repeat the command in step 3 , The result is shown in Fig. , The description has been deleted

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