MySQL's unique index unique

The purpose of creating a unique index is not to increase access speed, but to avoid duplication of data. A unique index can have more than one but the value of the indexed column must be unique, and the value of the indexed column allows for a null value. If you can determine that a data column will contain only values that are different from each other, you should use the keyword unique when creating an index for that data column and define it as a unique index.

Methods for creating unique cables

Action table

CREATE TABLE ' wb_blog ' (        ' id ' smallint (8) unsigned not NULL,        ' catid ' smallint (5) unsigned not N ULL default ' 0 ',        ' title ' varchar (+) NOT null DEFAULT ' ',        ' content ' text is not NULL,         PRIMARY KEY (' Id '),       )

1. Create a unique cable can be created with the table using the keyword unique

mysql> CREATE TABLE ' Wb_blog ' (     -   id ' smallint (8) unsigned not NULL,        ' CatID ' smallint (5) unsigned NOT null default ' 0 ',        ' title ' varchar (+) NOT null default ', 
       , ' content ' text not NULL,        PRIMARY KEY (' id '),         UNIQUE KEY ' catename ' (' catid ')     0 rows affected (0.24 sec)

The above code creates a unique index named Catename for the ' CATID ' field of the Wb_blog table

2. Create a table after creating it using the Create command

Mysql>0 rows affected (0.47 sec)

If you do not need a unique index, you can delete this

Mysql>0 rows affected (0.85 sec)

MySQL's unique index unique