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Introduction - Sequences

Introduction - Sequences -- Sequences and auto-incrementing

Description

Sequences are a way of offering unique IDs for data rows. If you do most of your work with e.g. MySQL, think of sequences as another way of doing AUTO_INCREMENT.

It's quite simple, first you request an ID, and then you insert that value in the ID field of the new row you're creating. You can have more than one sequence for all your tables, just be sure that you always use the same sequence for any particular table. To get the value of this unique ID use nextId(), if a sequence doesn't exists, it will be created automatically.

The sequence is automatically incremented each time nextId() is called.

Example 33-1. Using a sequence

<?php
// Once you have a valid DB object named $db...
$id = $db->nextId('mySequence');
if (PEAR::isError($id)) {
    die($id->getMessage());
}

// Use the ID in your INSERT query
$res =& $db->query("INSERT INTO myTable (id, text) VALUES ($id, 'foo')");
?>

Note

Warning

When using PEAR DB's sequence methods, we strongly advise using these methods for all procedures, including the creation of the sequences. Do not use PEAR DB's methods to access sequences that were created directly in the DBMS.

If you have a compelling reason to ignore this advice, be aware that the $seq_name argument given to all of PEAR DB's sequence methods are modified before DB calls the underlying DBMS.

$seq_name is passed through PHP's sprintf() function using the value from the seqname_format option as sprintf()'s format argument. The default seqname_format is %s_seq. So, for example, if you use person_id_sequence as the $seq_name, PEAR DB will change that name to person_id_sequence_seq when querying the DBMS about creating/accessing/updating the sequence.

The seqname_format can be modified when connect()'ing or via setOption().

See

createSequence(), nextId(), dropSequence()

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