How can I count the numbers of rows that a MySQL query returned?

Question

How can I count the number of rows that a MySQL query returned?

Answer 1

As it is 2015, and deprecation of mysql_* functionality, this is a PDO-only visualization.

';
    try {
        $theCategory="fruit";   // value from user, hard-coded here to get one in

        $dbh = new PDO("mysql:host=$host;dbname=$dbname;charset=utf8", $username, $password);
        $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        // prepared statement with named placeholders
        $stmt = $dbh->prepare("select id,foodName from foods where category=:theCat and perishable=1");
        $stmt->bindParam(':theCat', $theCategory, PDO::PARAM_STR,20);
        $stmt->execute();
        echo "rowCount() returns: ".$stmt->rowCount().$b;   // See comments below from the Manual, varies from driver to driver

        $stmt = $dbh->prepare("select count(*) as theCount from foods where category=:theCat and perishable=1");
        $stmt->bindParam(':theCat', $theCategory, PDO::PARAM_STR,20);
        $stmt->execute();
        $row=$stmt->fetch();    // fetches just one row, which is all we expect
        echo "count(*) returns: ".$row['theCount'].$b;

        $stmt = null;
        // PDO closes connection at end of script
    } catch (PDOException $e) {
        echo 'PDO Exception: ' . $e->getMessage();
        exit();
    }
?>

Schema for testing

create table foods
(   id int auto_increment primary key,
    foodName varchar(100) not null,
    category varchar(20) not null,
    perishable int not null
);
insert foods (foodName,category,perishable) values 
('kiwi','fruit',1),('ground hamburger','meat',1),
('canned pears','fruit',0),('concord grapes','fruit',1);

For my implementation, I get the output of 2 for both echos above. The purpose of the above 2 strategies is to determine if your driver implementation emits the rowCount, and if not, to seek a fall-back strategy.

From the Manual on PDOStatement::rowCount:

PDOStatement::rowCount() returns the number of rows affected by a DELETE, INSERT, or UPDATE statement.

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned. Your application can then perform the correct action.