Introduction - Fetch

Introduction - Fetch

Introduction - Fetch -- Fetching rows from the query

Description

Fetch rows by number

The PEAR MDB fetch system also supports an extra parameter to the fetch statement. So you can fetch rows from a result by number. This is especially helpful if you only want to show sets of an entire result (for example in building paginated HTML lists), fetch rows in an special order, etc.

Freeing the result set

It is recommended to finish the result set after processing in order to to save memory. Use freeResult() to do this.

Quick data retrieving

MDB provides some special ways to retrieve information from a query without the need of using fetch*() and loop throw results.

queryOne() retrieves the first result of the first column from a query
$numrows = $db->queryOne('select count(id) from clients');

queryRow() returns the first row and returns it as an array.
$sql = 'select name, address, phone from clients where id=1';
if (is_array($row = $db->queryRow($sql))) {
    list($name, $address, $phone) = $row;
}

queryCol() returns an array with the data of the selected column. It accepts the column number to retrieve as the second parameter.
$all_client_names = $db->queryCol('SELECT name FROM clients');
The above sentence could return for example:
$all_client_names = array('Stig', 'Jon', 'Colin');

getAll() fetches all the rows returned from a query. This method also has some advanced parameters still will also enable you to return the data as an associative array using the first column as the key.
$data = getAll('SELECT id, text, date FROM mytable');
/*
Will return:
array(
   1 => array('4', 'four', '2004'),
   2 => array('5', 'five', '2005'),
   3 => array('6', 'six', '2006')
)
*/

The query*() family methods will do all the dirty job for you, this is: launch the query, fetch the data and free the result. Please note that as all PEAR MDB functions they will return a MDB_Error object on errors.

Getting more information from query results

With MDB you have many ways to retrieve useful information from query results. These are:

  • numRows() : Returns the total number of rows returned from a "SELECT" query.
    // Number of rows
    echo $db->numRows($res);

  • numCols() : Returns the total number of columns returned from a "SELECT" query.
    // Number of cols
    echo $db->numCols($res);

  • affectedRows() : Returns the number of rows affected by a data manipulation query ("INSERT", "UPDATE" or "DELETE").
    // remember that this statement won't return a result object
    $db->query('DELETE * FROM clients');
    echo 'I have deleted ' . $db->affectedRows() . ' clients';

  • tableInfo() : Returns an associative array with information about the returned fields from a "SELECT" query.
    // Table Info
    print_r($db->tableInfo($res));

Don't forget to check if the returned result from your action is a MDB_Error object. If you get a error message like "MDB_Error: database not capable", means that your database backend doesn't support this action.

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