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This article mainly tells you how to add an index to mysql. You can look up the relevant professional terms on the Internet or find some related books to supplement them. Here, we will not dabble in, go straight to the topic, and hope to bring you some practical help.

1. Add PRIMARY KEY (primary key index)

Mysql > ALTER TABLE `table_ name` ADD PRIMARY KEY (`column`)

2. Add UNIQUE (unique index)

Mysql > ALTER TABLE `table_ name` ADD UNIQUE (`column`)

3. Add INDEX (general index)

Mysql > ALTER TABLE `table_ name` ADD INDEX index_name (`column`)

4. Add FULLTEXT (full-text index)

Mysql > ALTER TABLE `table_ name` ADD FULLTEXT (`column`)

5. Add multi-column index

Mysql > ALTER TABLE `table_ name` ADD INDEX index_name (`column1`, `column2`, `column3`)

Here is a more detailed approach

The alter table SQL statement can be used in MySQL to add indexes to the fields in the table.

The basic syntax for using the alter table statement to index fields in a table is:

ALTER TABLE ADD INDEX ()

Example: let's try to add an index to the t_name field in test.

Mysql > alter table test add index (t_name); Query OK, 0 rows affected (0.17 sec) Records: 0 Duplicates: 0 Warnings: 0

After the implementation is successful, let's take a look at the results.

Mysql > describe test +-+ | Field | Type | Null | Key | Default | Extra | + -+-+ | t_id | int (11) | YES | | NULL | | t_name | varchar (50) | NO | MUL | NULL | | t_password | char (32) | YES | | NULL | | t_birth | date | YES | | NULL | | +-| +-+ 4 rows in set (0.00 sec)

As a result, you can see that the Key column of the t_name field has changed from blank to MUL. What does this MUL mean? To explain briefly: if Key is MUL, then the value of the column can be repeated, and the column is the leading column of a non-unique index (the first column) or part of a unique index but can contain a null value of NULL.

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