AkinaCygapb-007и только если нет обоих – искуственно создается автонумератор.
Вы неверно прочитали мануал. Этот "внутренний автонумератор" в таблицах InnoDb есть ВСЕГДА. И ещё одно - доступ к нему получить НЕЛЬЗЯ. В принципе.Позвольте все же не согласиться...
http://dev.mysql.com/doc/refman/5.6/en/innodb-table-and-index.html 14.2.3.12.2. Clustered and Secondary Indexes
Every InnoDB table has a special index called the clustered index where the data for the rows is stored. Typically, the clustered index is synonymous with the primary key. To get the best performance from queries, inserts, and other database operations, you must understand how InnoDB uses the clustered index to optimize the most common lookup and DML operations for each table.
When you define a PRIMARY KEY on your table, InnoDB uses it as the clustered index. Define a primary key for each table that you create. If there is no logical unique and non-null column or set of columns, add a new auto-increment column, whose values are filled in automatically.
If you do not define a PRIMARY KEY for your table, MySQL locates the first UNIQUE index where all the key columns are NOT NULL and InnoDB uses it as the clustered index.
If the table has no PRIMARY KEY or suitable UNIQUE index , InnoDB
internally generates a hidden clustered index on a synthetic column containing row ID values. The rows are ordered by the ID that InnoDB assigns to the rows in such a table. The row ID is a 6-byte field that increases monotonically as new rows are inserted. Thus, the rows ordered by the row ID are physically in insertion order. там же, далее
How Secondary Indexes Relate to the Clustered Index
All indexes other than the clustered index are known as secondary indexes. In InnoDB,
each record in a secondary index contains the primary key columns for the row, as well as the columns specified for the secondary index. InnoDB uses this primary key value to search for the row in the clustered index.
If the primary key is long, the secondary indexes use more space, so it is advantageous to have a short primary key.
