sql - MySQL equivalent of Oracle's SEQUENCE.NEXTVAL

Question

I need to be able to generate run a query that will return the next value of ID on the following table:

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
)

In Oracle you can call NEXTVAL on a sequence and it gives you the next sequence (note: without having to do an insert on the table).

After googling around I found that you can find the current value of auto_increment by using the following query:

SELECT Auto_increment 
FROM information_schema.tables 
WHERE table_name='animals';

The problem is I would like the value to be increment every time the value is queried. In Oracle, when you call nextval, the value of the sequence is incremented even if you don't insert a row into a table.

Is there any way I can modify the above query so that the value returned will always be different from the last time the query was called? i.e. Auto_increment is incremented every time it is checked and when used on a query it would use a new value.

I am using Spring JDBCTemplate so if it can be done in one query the better.

Answer 1

http://docs.oracle.com/cd/E17952_01/refman-5.5-en/example-auto-increment.html

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 |
+----+---------+

No value was specified for the AUTO_INCREMENT column, so MySQL assigned sequence numbers automatically. You can also explicitly assign NULL or 0 to the column to generate sequence numbers.

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 values are not affected by another connection which is also performing inserts.

Use the smallest integer data type for the AUTO_INCREMENT column that is large enough to hold the maximum sequence value you will need. When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. Use the UNSIGNED attribute if possible to allow a greater range. For example, if you use TINYINT, the maximum permissible sequence number is 127. For TINYINT UNSIGNED, the maximum is 255. See Section 11.2.1, “Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types.

Note For a multiple-row insert, LAST_INSERT_ID() and mysql_insert_id() actually return the AUTO_INCREMENT key from the first of the inserted rows. This enables multiple-row inserts to be reproduced correctly on other servers in a replication setup.

If the AUTO_INCREMENT column is part of multiple indexes, MySQL generates sequence values using the index that begins with the AUTO_INCREMENT column, if there is one. For example, if the animals table contained indexes PRIMARY KEY (grp, id) and INDEX (id), MySQL would ignore the PRIMARY KEY for generating sequence values. As a result, the table would contain a single sequence, not a sequence per grp value.

To start with an AUTO_INCREMENT value other than 1, set that value with CREATE TABLE or ALTER TABLE, like this:

mysql> ALTER TABLE tbl AUTO_INCREMENT = 100; InnoDB Notes

For InnoDB tables, be careful if you modify the column containing the auto-increment value in the middle of a sequence of INSERT statements. For example, if you use an UPDATE statement to put a new, larger value in the auto-increment column, a subsequent INSERT could encounter a “Duplicate entry” error. The test whether an auto-increment value is already present occurs if you do a DELETE followed by more INSERT statements, or when you COMMIT the transaction, but not after an UPDATE statement.

MyISAM Notes

For MyISAM 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)
) ENGINE=MyISAM;

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 |
+--------+----+---------+

In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are 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.

Further Reading

More information about AUTO_INCREMENT is available here:

How to assign the AUTO_INCREMENT attribute to a column: Section 13.1.17, “CREATE TABLE Syntax”, and Section 13.1.7, “ALTER TABLE Syntax”.

How AUTO_INCREMENT behaves depending on the NO_AUTO_VALUE_ON_ZERO SQL mode: Section 5.1.7, “Server SQL Modes”.

How to use the LAST_INSERT_ID() function to find the row that contains the most recent AUTO_INCREMENT value: Section 12.14, “Information Functions”.

Setting the AUTO_INCREMENT value to be used: Section 5.1.4, “Server System Variables”.

AUTO_INCREMENT and replication: Section 16.4.1.1, “Replication and AUTO_INCREMENT”.

Server-system variables related to AUTO_INCREMENT (auto_increment_increment and auto_increment_offset) that can be used for replication: Section 5.1.4, “Server System Variables”.

http://search.oracle.com/search/search?q=auto_increment&group=Documentation&x=0&y=0