An index in MySQL can be added using ALTER statement in multiple ways as shown:
| ALTER TABLE tbl_name ADD PRIMARY KEY (column_list) ALTER TABLE tbl_name ADD UNIQUE index_name (columnlist) ALTER TABLE tbl_name ADD INDEX index_name (column_list) ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list) |
Drop:
| ALTER TABLE table_name DROP PRIMARY KEY; |
In order to drop an index that is not a primary key, the name of index should be specified.
Index in a database is used to improve the speed of operations in a table. Index can be done using single or multiple columns.
There are 4 types of index commands to adding indexes to a table:
| 1. ALTER TABLE tbl_name ADD PRIMARY KEY (column_list) : Adds a primary key which means adds indexes and does not allow null values. 2. ALTER TABLE tbl_name ADD UNIQUE index_name (column_list) : Creates an index whose values must be null with the exception of NULL values. 3. ALTER TABLE tbl_name ADD INDEX index_name (column_list) : Adds indexes in which one value can appear more than once 4. ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list) : Adds an index for efficient text-searching purpose. |
Dropping indexes:
To drop a primary key:
| ALTER TABLE testalter_tbl DROP PRIMARY KEY; |
To drop an index:
| DROP INDEX index_name ON tbl_name. |
原文：http://www.cnblogs.com/maoxiaolv/p/5526472.html