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The initial sequence value cannot be set with an AUTO_INCREMENT = n option in the CREATE TABLE statement. Nor can it be modified using that option with ALTER TABLE.
Values that are deleted from the top of the sequence are reused.
Composite indexes can be used to generate multiple independent sequences within a table.
AUTO_INCREMENT for InnoDB Tables
The InnoDB table handler manages AUTO_INCREMENT columns as follows:
The initial sequence value cannot be set with an AUTO_INCREMENT = n option in the CREATE TABLE statement. Nor can it be modified using that option with ALTER TABLE.
Values that are deleted from the top of the sequence are not reused.
Composite indexes cannot be used to generate multiple independent sequences within a table.
Issues to Consider with AUTO_INCREMENT
You should keep the following points in mind to avoid being surprised when you use AUTO_INCREMENT columns:
AUTO_INCREMENT is not a column type; it's a column type attribute. Furthermore, AUTO_INCREMENT is an attribute intended for use only with integer types. Versions of MySQL earlier than 3.23 are lax in enforcing this constraint and will let you declare a column type such as CHAR with the AUTO_INCREMENT attribute. However, only the integer types work correctly as AUTO_INCREMENT columns.
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