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Notes 10.4.5 Sequences
Not every RDBMS has the ability to assign unique row IDs, and those that do have wildly
differing ways of returning that information. PEAR DB sequences are an alternative to database-
specific ID assignment (for instance, MySQL’sAUTO_INCREMENT).
The nextID( ) method returns the next ID for the given sequence:
$id = $db->nextID(sequence);
Normally you will have one sequence per table for which you want unique IDs. This example
inserts values into the books table, giving a unique identifier to each row:
$books = array(array(‘Foundation’, 1951),

array(‘Second Foundation’, 1953),
array(‘Foundation and Empire’, 1952));

foreach ($books as $book) {
$id = $db->nextID(‘books’);
splice($book, 0, 0, $id);

$db->query(‘INSERT INTO books (bookid,title,pub_year) VALUES (?,?,?)’, $book);
}

A sequence is really a table in the database that keeps track of the last-assigned ID. You can
explicitly create and destroy sequences with the createSequence( ) and dropSequence( ) methods:

$res = $db->createSequence(sequence);
$res = $db->dropSequence(sequence);

The result will be the result object from the create or drop query or DB_ERROR if an error
occurred.

Create a database and a sequence. Write the command to delete sequence from
the database.

10.4.6 Metadata
The getListOf( ) method lets you query the database for information on available databases,
users, views, and functions:
$data = $db->getListOf(what);

The what parameter is a string identifying the database feature to list. Most databases support
“databases;” some support “users,” “views,” and “functions.”

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