mysql 索引操作

6.4 mysql表的索引操作

6.4.1 创建索引

    方式一（create）：
    创建普通索引：create index indexName on tableName(列名)
    创建唯一索引：create unique index indexName on tableName(列名)
    方式二(alter):
    创建普通索引：alter table tableName add index indexName(列名)
    创建唯一索引：alter table tableName add unique(列名)
    创建主键索引: alter table tableName add primary key (列名)

# 实验一：使用（create）将student表的id设置为索引

    mysql> show index from student\G;
    Empty set (0.00 sec)

    mysql> create index stu_index_id on student(id);
    Query OK, 4 rows affected (0.01 sec)
    Records: 4  Duplicates: 0  Warnings: 0

    mysql> show index from student\G;
    *************************** 1. row ***************************
           Table: student
      Non_unique: 1
        Key_name: stu_index_id
    Seq_in_index: 1
     Column_name: id
       Collation: A
     Cardinality: NULL
        Sub_part: NULL
          Packed: NULL
            Null: YES
      Index_type: BTREE
         Comment: 
    1 row in set (0.00 sec)

# 实验二：使用（alter）将student3表的id设置为索引

    mysql> show index from student3\G;
    Empty set (0.00 sec)

    mysql> mysql> alter table student3 add index stu3_index_id (id);
    Query OK, 0 rows affected (0.03 sec)
    Records: 0  Duplicates: 0  Warnings: 0


    mysql> show index from student3\G;
    *************************** 1. row ***************************
           Table: student3
      Non_unique: 1
        Key_name: stu3_index_id
    Seq_in_index: 1
     Column_name: id
       Collation: A
     Cardinality: NULL
        Sub_part: NULL
          Packed: NULL
            Null: YES
      Index_type: BTREE
         Comment: 
    1 row in set (0.00 sec)

注意：创建唯一索引的时候，该列中不能出现重复值否则索引创建不成功

6.4.2 删除索引

    方式一(drop):
    删除普通索引和唯一索引：drop index indexName on tableName;
    方式二(alter):
    删除普通索引和唯一索引：alter table tableName drop index indexName;
    删除主键索引:alter table tableName drop primary key

# 实验一 使用方式一删除student索引：

    mysql> drop index stu_index_id on student;
    Query OK, 4 rows affected (0.00 sec)
    Records: 4  Duplicates: 0  Warnings: 0

    mysql> show index from student;
    Empty set (0.00 sec)

# 实验三 使用方式二删除student3索引：

    mysql> alter table student3 drop index stu3_index_id;
    Query OK, 0 rows affected (0.00 sec)
    Records: 0  Duplicates: 0  Warnings: 0

    mysql> show index from student3;
    Empty set (0.00 sec)