Now that you have an AUTO_INCREMENT column, you want to use it to generate a new sequence value.
Insert NULL into the column, or just omit it from your INSERT statement. Either way, MySQL will create a new sequence number for you.
One of the useful properties of an AUTO_INCREMENT column is that you don't have to assign its values yourselfMySQL does so for you. There are two ways to generate new AUTO_INCREMENT values, demonstrated here using the id column of the insect table. First, you can explicitly set the id column to NULL. The following statement inserts the first four of Junior's specimens into the insect table this way:
 Setting an AUTO_INCREMENT column to zero currently has the same effect as setting it to NULL. But that is not guaranteed to be true in the future, so it's better to use NULL.
mysql> INSERT INTO insect (id,name,date,origin) VALUES -> (NULL,'housefly','2001-09-10','kitchen'), -> (NULL,'millipede','2001-09-10','driveway'), -> (NULL,'grasshopper','2001-09-10','front yard'), -> (NULL,'stink bug','2001-09-10','front yard');
Second, you can omit the id column from the INSERT statement entirely. In MySQL, you can create new records without explicitly specifying values for every column. MySQL assigns default values to the missing columns automatically, and the default for an AUTO_INCREMENT column happens to be the next sequence number. Thus, you can insert records into the insect table without naming the id column at all. This statement adds Junior's other four specimens to the insect table that way:
mysql> INSERT INTO insect (name,date,origin) VALUES -> ('cabbage butterfly','2001-09-10','garden'), -> ('ant','2001-09-10','back yard'), -> ('ant','2001-09-10','back yard'), -> ('millbug','2001-09-10','under rock');
Whichever method you use, MySQL determines the next sequence number for each record and assigns it to the id column, as you can verify for yourself:
mysql> SELECT * FROM insect ORDER BY id; +----+-------------------+------------+------------+ | id | name | date | origin | +----+-------------------+------------+------------+ | 1 | housefly | 2001-09-10 | kitchen | | 2 | millipede | 2001-09-10 | driveway | | 3 | grasshopper | 2001-09-10 | front yard | | 4 | stink bug | 2001-09-10 | front yard | | 5 | cabbage butterfly | 2001-09-10 | garden | | 6 | ant | 2001-09-10 | back yard | | 7 | ant | 2001-09-10 | back yard | | 8 | millbug | 2001-09-10 | under rock | +----+-------------------+------------+------------+
As Junior collects more specimens, you can add more records to the table and they'll be assigned the next values in the sequence (9, 10, ...).
The concept underlying AUTO_INCREMENT columns is simple enough in principle: each time you create a new row, MySQL generates the next number in the sequence and assigns it to the row. But there are certain subtleties to know about, as well as differences in how AUTO_INCREMENT sequences are handled for different table types. By being aware of these issues, you can use sequences more effectively and avoid surprises. For example, if you explicitly set the id column to a non-NULL value, one of two things happens:
mysql> INSERT INTO insect (id,name,date,origin) VALUES -> (3,'cricket','2001-09-11','basement'); ERROR 1062 at line 1: Duplicate entry '3' for key 1
This happens because when you create an AUTO_INCREMENT column, you must declare it to be either a PRIMARY KEY or a UNIQUE index. As a result, it cannot contain duplicate values.
Now let's look in more detail at how to define AUTO_INCREMENT columns and how they behave.
Using the mysql Client Program
Writing MySQL-Based Programs
Record Selection Techniques
Working with Strings
Working with Dates and Times
Sorting Query Results
Modifying Tables with ALTER TABLE
Obtaining and Using Metadata
Importing and Exporting Data
Generating and Using Sequences
Using Multiple Tables
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