MYSQL ALTER

Posted 2020-07-12 木子三金

ALTER command to add and drop INDEX in mysql

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.

ALTER command to add and drop INDEX in MySQL

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.