MySQL non-clustered index && level two index && secondary index

MySQL non-clustered index && level two index && secondary index

Each table in MySQL has a clustered index (clustered index), except that each nonclustered index on the table is a level two index, also known as a secondary index (secondary indexes).

For InnoDB, each InnoDB table has a special index called a clustered index. If you have a primary key defined on your table, the primary key index is a clustered index. If you do not define a primary key for your table, MySQL takes the first unique index (unique) and contains only non-empty columns (not NULL) as the primary key, and InnoDB uses it as a clustered index. Without such a column, InnoDB itself produces an ID value that has six bytes and is hidden as the clustered index.

Clustered index: http://my.oschina.net/xinxingegeya/blog/474895

The following are either two-level indexes, or secondary indexes, except the primary key.

> show create table article***  1. row *********************       table:  articleCreate Table: CREATE TABLE  ' article '   (   ' id '  int (11)  NOT NULL AUTO_INCREMENT,   ' title '  varchar (255)  NOT NULL,   ' ShortName '  varchar (255)  NOT NULL,   ' Authorid '  int (one)  NOT NULL,    ' createtime '  datetime NOT NULL,   ' state '  int (one)  NOT NULL,    ' Totalview '  int (one)  DEFAULT NULL,  PRIMARY KEY  (' id '),   unique key  ' Idx_short_name_title '   (' title ', ' ShortName '),  key  ' idx_author_id '   (' Authorid ')  ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=latin11 rows  In set 

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MySQL non-clustered index && level two index && secondary index