PHP MySQL: Querying Data from Database
Summary: in this tutorial, you will learn how to query data from the MySQL database by using PHP PDO. You will also learn how to use PDO prepared statements to select data securely.
PHP MySQL Querying data using simple SELECT statement
To query data from the MySQL database, follow the steps below:
First, connect to a MySQL database. Check it out the connecting to MySQL database using PDO tutorial for detail information.
$pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);Then, construct a SELECT statement and execute it by using the query() method of the PDO object.
$sql = 'SELECT lastname, firstname, jobtitle
FROM employees
ORDER BY lastname';
$q = $pdo->query($sql);The query() method of the PDO object returns a PDOStatement object, or false on failure.
Next, set the PDO::FETCH_ASSOC fetch mode for the PDOStatement object by using the setFetchMode() method. The PDO::FETCH_ASSOC mode instructs the fetch() method to return a result set as an array indexed by column name.
$q->setFetchMode(PDO::FETCH_ASSOC);
After that, fetch each row from the result set until there is no row left by using the fetch() method of the PDOStatement object.
Putting it all together.
<?php
require_once 'dbconfig.php';
try {
$pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);
$sql = 'SELECT lastname,
firstname,
jobtitle
FROM employees
ORDER BY lastname';
$q = $pdo->query($sql);
$q->setFetchMode(PDO::FETCH_ASSOC);
} catch (PDOException $e) {
die("Could not connect to the database $dbname :" . $e->getMessage());
}
?>
<!DOCTYPE html>
<html>
<head>
<title>PHP MySQL Query Data Demo</title>
<link href="css/bootstrap.min.css" rel="stylesheet">
<link href="css/style.css" rel="stylesheet">
</head>
<body>
<div id="container">
<h1>Employees</h1>
<table class="table table-bordered table-condensed">
<thead>
<tr>
<th>First Name</th>
<th>Last Name</th>
<th>Job Title</th>
</tr>
</thead>
<tbody>
<?php while ($row = $q->fetch()): ?>
<tr>
<td><?php echo htmlspecialchars($row['lastname']) ?></td>
<td><?php echo htmlspecialchars($row['firstname']); ?></td>
<td><?php echo htmlspecialchars($row['jobtitle']); ?></td>
</tr>
<?php endwhile; ?>
</tbody>
</table>
</body>
</div>
</html>PHP MySQL Querying data using PDO prepared statement
In practice, we often pass the argument from PHP to the SQL statement e.g., get the employee whose last name ends with son . To do it securely and avoid SQL injection attacks, you need to use the PDO prepared statement.
Let’s take a look at the following example:
<?php
require_once 'dbconfig.php';
try {
$pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);
$sql = 'SELECT lastname,
firstname,
jobtitle
FROM employees
WHERE lastname LIKE ?';
$q = $pdo->prepare($sql);
$q->execute(['%son']);
$q->setFetchMode(PDO::FETCH_ASSOC);
while ($r = $q->fetch()) {
echo sprintf('%s <br/>', $r['lastname']);
}
} catch (PDOException $pe) {
die("Could not connect to the database $dbname :" . $pe->getMessage());
}How the script works.
- First, we use a question mark (?) in the
SELECTstatement. PDO will replace the question mark in the query with the corresponding argument. The question mark is called a positional placeholder. - Next, we call the
prepare()method of the PDO object to prepare the SQL statement for the execution. - Then, we execute the statement by calling the
execute()method of thePDOStatementobject. In addition, we pass an argument as an array to replace the placeholder in theSELECTstatement. By doing this, theSELECTstatement will be translated as follows:
SELECT lastname,
firstname,
jobtitle
FROM employees
WHERE lastname LIKE '%son';- After that, we set the fetch mode for the
PDOStatementobject. - Finally, we fetch each row of the result set and display the last name field.
PHP provides you with another way to use placeholders in the prepared statement called named placeholder. The advantages of using the named placeholder are:
- More descriptive.
- If the SQL statement has multiple placeholders, it is easier to pass the arguments to the
execute()method.
Let’s take a look at the following example:
<?php
require_once 'dbconfig.php';
try {
$pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);
$sql = 'SELECT lastname,
firstname,
jobtitle
FROM employees
WHERE lastname LIKE :lname OR
firstname LIKE :fname;';
// prepare statement for execution
$q = $pdo->prepare($sql);
// pass values to the query and execute it
$q->execute([':fname' => 'Le%',
':lname' => '%son']);
$q->setFetchMode(PDO::FETCH_ASSOC);
// print out the result set
while ($r = $q->fetch()) {
echo sprintf('%s <br/>', $r['lastname']);
}
} catch (PDOException $e) {
die("Could not connect to the database $dbname :" . $e->getMessage());
}The :lname and :fname are the named placeholders. They are substituted by the corresponding argument in the associative array that we pass to the execute method.
In this tutorial, you have learned how to query data from the MySQL database using PDO objects.
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