(mysql.info.gz) example-AUTO_INCREMENT
Info Catalog
(mysql.info.gz) Calculating days
(mysql.info.gz) Examples
3.6.9 Using `AUTO_INCREMENT'
----------------------------
The `AUTO_INCREMENT' attribute can be used to generate a unique
identity for new rows:
CREATE TABLE animals (
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (id)
);
INSERT INTO animals (name) VALUES ('dog'),('cat'),('penguin'),
('lax'),('whale'),('ostrich');
SELECT * FROM animals;
Which returns:
+----+---------+
| id | name |
+----+---------+
| 1 | dog |
| 2 | cat |
| 3 | penguin |
| 4 | lax |
| 5 | whale |
| 6 | ostrich |
+----+---------+
You can retrieve the most recent `AUTO_INCREMENT' value with the
`LAST_INSERT_ID()' SQL function or the `mysql_insert_id()' C API
function. These functions are connection-specific, so their return value
is not affected by another connection also doing inserts.
Note: For a multiple-row insert, `LAST_INSERT_ID()'/`mysql_insert_id()'
will actually return the `AUTO_INCREMENT' key from the *first* of the
inserted rows. This allows multiple-row inserts to be reproduced
correctly on other servers in a replication setup.
For `MyISAM' and `BDB' tables you can specify `AUTO_INCREMENT' on a
secondary column in a multiple-column index. In this case, the
generated value for the `AUTO_INCREMENT' column is calculated as
`MAX(auto_increment_column)+1 WHERE prefix=given-prefix'. This is
useful when you want to put data into ordered groups.
CREATE TABLE animals (
grp ENUM('fish','mammal','bird') NOT NULL,
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (grp,id)
);
INSERT INTO animals (grp,name) VALUES('mammal','dog'),('mammal','cat'),
('bird','penguin'),('fish','lax'),('mammal','whale'),
('bird','ostrich');
SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
| bird | 2 | ostrich |
+--------+----+---------+
Note that in this case (when the `AUTO_INCREMENT' column is part of a
multiple-column index), `AUTO_INCREMENT' values will be reused if you
delete the row with the biggest `AUTO_INCREMENT' value in any group.
This happens even for `MyISAM' tables, for which `AUTO_INCREMENT'
values normally are not reused.)
Info Catalog
(mysql.info.gz) Calculating days
(mysql.info.gz) Examples
automatically generated byinfo2html