MySQL equivalent of Oracle's SEQUENCE.NEXTVAL

Solution 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.

Solution 2:

This example with InnoDB demonstrates a way to implement your own counter using interlocked queries:

http://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html

What do you need to create a gap for? To reserve IDs? I'd rather "fix" the design at all costs and update the other modules instead of touching a sequence.

Instead of just incrementing the sequence explicitly, I'd imply it by inserting a default row (marked invalid) for each id to allocate and return the id. This approach is consistent and portable. Later, instead of forcing inserts using an explicit sequence value, you can update these default rows by their matching sequence values. This requires more memory but no locks. Garbage collection on expired rows can help here. 'insert or update' statements can recreate garbage collected rows, I wouldn't do this though.

Solution 3:

You could add your own MySQL function - as demonstrated at http://www.microshell.com/database/mysql/emulating-nextval-function-to-get-sequence-in-mysql/ - allowing you to do something like this:

SELECT nextval('sq_my_sequence') as next_sequence;

Solution 4:

MySQL uses AUTO_INCREMENT which serves the purposes. But there are below differences:

MySQL AUTO_INCREMENT to Oracle SEQUENCE Differences

AUTO_INCREMENT is limited to one column per table
AUTO_INCREMENT must be assigned to a specific table.column (not allowing multi table use)
AUTO_INCREMENT is INSERTed as a not specified column, or a value of NULL

if you would like to see a SEQUENCE implementation with MySQL , can do with SP.

Refer below link explained everything you want.

http://ronaldbradford.com/blog/sequences-in-mysql-2006-01-26/

Solution 5:

You want the next value on THAT table so that you can make rows which aren't yet inserted without disturbing other processes which are using the auto-increment?

Some options:

Go ahead and just insert the rows to "use up the sequence", mark them as pending and then update them later.

Insert in a transaction and abort the transaction - the auto-number sequence should get used up and make a "gap" in the table normally - that number is now free for you to use.

With Oracle, the sequence is completely independent of table, so processes can use the sequence or not (and they can also use the same sequence for different tables). In that vein, you could implement a sequence-only table which you access through some kind of function, and for the other processes which need to rely on the auto-increment, remove the auto-increment and use a trigger which assigns from the same sequence function if no id is provided.