PHP MySQL Where

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The WHERE clause filters records based on specified conditions.

The basic syntax of the WHERE clause is as follows:

SELECT column_name(s) FROM table_name WHERE column_name operator value

Let's create a SQL query using the WHERE clause in a SELECT statement. We'll execute this query by passing it to the PHP mysqli_query() function to retrieve filtered data.

Assume we have a persons table in the demo database with the following records:

+----+------------+-----------+----------------------+
| id | first_name | last_name | email                |
+----+------------+-----------+----------------------+
|  1 | Peter      | Parker    | peterparker@mail.com |
|  2 | John       | Rambo     | johnrambo@mail.com   |
|  3 | Clark      | Kent      | clarkkent@mail.com   |
|  4 | John       | Carter    | johncarter@mail.com  |
|  5 | Harry      | Potter    | harrypotter@mail.com |
+----+------------+-----------+----------------------+

The PHP code below retrieves all rows from the persons table where the first_name column equals 'john':

Example

Procedural Object Oriented PDO

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<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$link = mysqli_connect("localhost", "root", "", "demo");

// Check connection
if($link === false){
die("ERROR: Could not connect. " . mysqli_connect_error());
}

// Attempt select query execution
$sql = "SELECT * FROM persons WHERE first_name='john'";
if($result = mysqli_query($link, $sql)){
if(mysqli_num_rows($result) > 0){
echo "<table>";
echo "<tr>";
echo "<th>id</th>";
echo "<th>first_name</th>";
echo "<th>last_name</th>";
echo "<th>email</th>";
echo "</tr>";
while($row = mysqli_fetch_array($result)){
echo "<tr>";
echo "<td>" . $row['id'] . "</td>";
echo "<td>" . $row['first_name'] . "</td>";
echo "<td>" . $row['last_name'] . "</td>";
echo "<td>" . $row['email'] . "</td>";
echo "</tr>";
}
echo "</table>";
// Close result set
mysqli_free_result($result);
} else{
echo "No records matching your query were found.";
}
} else{
echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}

// Close connection
mysqli_close($link);
?>

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$mysqli = new mysqli("localhost", "root", "", "demo");

// Check connection
if($mysqli === false){
die("ERROR: Could not connect. " . $mysqli->connect_error);
}

// Attempt select query execution
$sql = "SELECT * FROM persons WHERE first_name='john'";
if($result = $mysqli->query($sql)){
if($result->num_rows > 0){
echo "<table>";
echo "<tr>";
echo "<th>id</th>";
echo "<th>first_name</th>";
echo "<th>last_name</th>";
echo "<th>email</th>";
echo "</tr>";
while($row = $result->fetch_array()){
echo "<tr>";
echo "<td>" . $row['id'] . "</td>";
echo "<td>" . $row['first_name'] . "</td>";
echo "<td>" . $row['last_name'] . "</td>";
echo "<td>" . $row['email'] . "</td>";
echo "</tr>";
}
echo "</table>";
// Free result set
$result->free();
} else{
echo "No records matching your query were found.";
}
} else{
echo "ERROR: Could not able to execute $sql. " . $mysqli->error;
}

// Close connection
$mysqli->close();
?>

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
try{
$pdo = new PDO("mysql:host=localhost;dbname=demo", "root", "");
// Set the PDO error mode to exception
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e){
die("ERROR: Could not connect. " . $e->getMessage());
}

// Attempt select query execution
try{
$sql = "SELECT * FROM persons WHERE first_name='john'";  
$result = $pdo->query($sql);
if($result->rowCount() > 0){
echo "<table>";
echo "<tr>";
echo "<th>id</th>";
echo "<th>first_name</th>";
echo "<th>last_name</th>";
echo "<th>email</th>";
echo "</tr>";
while($row = $result->fetch()){
echo "<tr>";
echo "<td>" . $row['id'] . "</td>";
echo "<td>" . $row['first_name'] . "</td>";
echo "<td>" . $row['last_name'] . "</td>";
echo "<td>" . $row['email'] . "</td>";
echo "</tr>";
}
echo "</table>";
// Free result set
unset($result);
} else{
echo "No records matching your query were found.";
}
} catch(PDOException $e){
die("ERROR: Could not able to execute $sql. " . $e->getMessage());
}

// Close connection
unset($pdo);
?>

After applying the filter, the result set will appear as follows:

+----+------------+-----------+---------------------+
| id | first_name | last_name | email               |
+----+------------+-----------+---------------------+
|  2 | John       | Rambo     | johnrambo@mail.com  |
|  4 | John       | Carter    | johncarter@mail.com |
+----+------------+-----------+---------------------+

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