Starting a Sequence at a Particular Value

11.12.1 Problem

Sequences start at 1, but you want to use a different starting value.

11.12.2 Solution

Add an AUTO_INCREMENT clause to your CREATE TABLE statement when you create the table. If the table has already been created, use an ALTER TABLE statement to set the starting value.

11.12.3 Discussion

By default, AUTO_INCREMENT sequences start at one:

mysql> CREATE TABLE t
 -> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id));
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> SELECT id FROM t ORDER BY id;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+

For MyISAM tables, you can begin the sequence at a specific initial value n by including an AUTO_INCREMENT = n clause at the end of the CREATE TABLE statement:

mysql> CREATE TABLE t
 -> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id))
 -> AUTO_INCREMENT = 100;
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> SELECT id FROM t ORDER BY id;
+-----+
| id |
+-----+
| 100 |
| 101 |
| 102 |
+-----+

Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE:

mysql> CREATE TABLE t
 -> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id));
mysql> ALTER TABLE t AUTO_INCREMENT = 100;
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> SELECT id FROM t ORDER BY id;
+-----+
| id |
+-----+
| 100 |
| 101 |
| 102 |
+-----+

To start a sequence at n for table types other than MyISAM, you must use a hack: insert a "fake" record with sequence value n-1, then delete it after inserting one or more "real" records. The following example illustrates how to start a sequence at 100 for an InnoDB table:

mysql> CREATE TABLE t
 -> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id))
 -> TYPE = InnoDB;
mysql> INSERT INTO t (id) VALUES(99);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> DELETE FROM t WHERE id = 99;
mysql> SELECT * FROM t ORDER BY id;
+-----+
| id |
+-----+
| 100 |
| 101 |
| 102 |
+-----+

Remember that if you clear out the contents of a table with a DELETE statement that has no WHERE clause, the sequence may be reset to begin with 1, even for types that normally do not reuse sequence values. (See Recipe 11.5.) In this case, you should reinitialize the sequence value explicitly after clearing the table if you don't want it to begin with 1.

Using the mysql Client Program

Writing MySQL-Based Programs

Record Selection Techniques

Working with Strings

Working with Dates and Times

Sorting Query Results

Generating Summaries

Modifying Tables with ALTER TABLE

Obtaining and Using Metadata

Importing and Exporting Data

Generating and Using Sequences

Using Multiple Tables

Statistical Techniques

Handling Duplicates

Performing Transactions

Introduction to MySQL on the Web

Incorporating Query Resultsinto Web Pages

Processing Web Input with MySQL

Using MySQL-Based Web Session Management

Appendix A. Obtaining MySQL Software

Appendix B. JSP and Tomcat Primer

Appendix C. References



MySQL Cookbook
MySQL Cookbook
ISBN: 059652708X
EAN: 2147483647
Year: 2005
Pages: 412
Authors: Paul DuBois

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