11.8 Extending the Range of a Sequence Column
11.8.1 Problem
You want to avoid resequencing
a column, but you're running out of room for new
sequence numbers.
11.8.2 Solution
See if you can make the column UNSIGNED or change
the column to use a larger integer type.
11.8.3 Discussion
Resequencing an AUTO_INCREMENT column changes the
contents of potentially every row in the table. It's
often possible to avoid this by extending the range of the column,
which changes the table's structure rather than its
contents:
If the column type is signed, make it UNSIGNED and
you'll double the range of available values. Suppose
you have an id column that currently is defined
like this:
id MEDIUMINT NOT NULL AUTO_INCREMENT The upper range of a signed MEDIUMINT column is
8,388,607. This can be increased to 16,777,215 by making the column
UNSIGNED with
ALTER TABLE:
ALTER TABLE tbl_name MODIFY id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT; If your column is already UNSIGNED and it is not
already the largest integer type (BIGINT),
converting it to a larger type increases its range. You can use
ALTER TABLE for this, too. For
example, the id column in the previous example can
be converted from MEDIUMINT to
BIGINT like so:
ALTER TABLE tbl_name MODIFY id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT;
Recipe 11.4 includes a table that shows the ranges
for each integer type, which you may find helpful in assessing which
type to use.
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