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                **1. 索引分類** * 單列索引:即一個索引只包含單個列,一個表可以有多個單列索引,但這不是組合索引。 * 組合索引:即一個索引包含多個列。 >[info]提醒:主鍵本身就是一個索引、unique的列本身也是一個索引。 **2. 創建索引方式** >[warning]索引名稱`indexName`自定義,但要保證在一張表中唯一 (1)創建方式1:`create`語句創建。 ```sql # 單列索引 mysql> create index indexName on tableName(column_name); # 組合索引 mysql> create index indexName on tableName(column_list); # 唯一索引 mysql> create unique index indexName on tableName(column_list); # 主鍵索引 mysql> ceate primary key index indexName on tableName(column_list) ``` (2)創建方式2:建表時就添加索引。 ```sql mysql> create table tableName( id varchar(255) primary key not null, # 主鍵本身就是一個單列索引 card varchar(255) unique not null, # unique 聲明的列本身就是一個單列索引 name varchar(255), age int, index indexName(name, age) # 創建索引 ) ``` (3)通過`alter`命令添加索引。 ```sql mysql> alter table tableName add primary key indexName(column_list); mysql> alter table tableName add unique indexName(column_list); mysql> alter table tableName add index indexNamei(column_list); #全文索引 mysql> alter table tableName add fulltext indexName(column_list); ``` **3. 刪除索引** ```sql (1)方式1 mysql> drop index indexName on tableName; (2)方式2 mysql> alter table tableName drop index indexName; ``` **4. 查看一張表的所有索引** ```sql mysql> show index from student; +---------+------------+-----------+--------------+-------------+-----------+-------------+... | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | S... +---------+------------+-----------+--------------+-------------+-----------+-------------+... | student | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | ... | student | 0 | indexName | 1 | name | A | 1 | NULL | NULL | Y... | student | 0 | indexName | 2 | sex | A | 1 | NULL | NULL | YES... +---------+------------+-----------+--------------+-------------+-----------+-------------+... ``` **** 參考文檔:https://www.runoob.com/mysql/mysql-index.html
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