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PHP MySQL Use WHERE – Complete Beginner Tutorial

The WHERE clause is one of the most important parts of MySQL queries. It allows you to filter records and retrieve or update only the data you need. Without WHERE, database operations can affect all records, which is often dangerous.

This tutorial explains how to use the WHERE clause in PHP MySQL with practical examples and outputs.

What Is WHERE Clause in PHP MySQL?

The WHERE clause is used to specify conditions in SQL queries. It filters records based on given criteria.

Basic SQL syntax:

SELECT * FROM table_name WHERE condition;

Only the rows that match the condition are affected.

Why WHERE Clause Is Important in PHP MySQL

The WHERE clause helps to:

Retrieve specific records
Update selected rows
Delete selected rows
Improve performance
Prevent accidental data changes

Almost every real-world PHP application uses WHERE conditions.

Prerequisites for Using WHERE in PHP

Before using WHERE, ensure you have:

PHP installed
MySQL database
A database connection file
A table with records

Sample MySQL Table Used in Examples

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100),
    age INT
);

PHP MySQL Database Connection Code

<?php
$conn = mysqli_connect("localhost", "root", "", "testdb");

if (!$conn) {
    die("Database connection failed");
}
?>

Select Data Using WHERE Clause in PHP MySQL

<?php
$query = "SELECT * FROM users WHERE id = 1";
$result = mysqli_query($conn, $query);

$row = mysqli_fetch_assoc($result);
echo $row['name'];
?>

Output:

Rahul

Using WHERE with String Values in PHP MySQL

<?php
$query = "SELECT * FROM users WHERE name = 'Amit'";
$result = mysqli_query($conn, $query);

while ($row = mysqli_fetch_assoc($result)) {
    echo $row['email'];
}
?>

Output:

amit@gmail.com

WHERE Clause with Comparison Operators

Common operators:

= equal
> greater than
< less than
>= greater than or equal
<= less than or equal

Example:

<?php
$query = "SELECT * FROM users WHERE age > 25";
$result = mysqli_query($conn, $query);

while ($row = mysqli_fetch_assoc($result)) {
    echo $row['name'] . "<br>";
}
?>

Output:

Amit

Using WHERE with AND Condition in PHP MySQL

<?php
$query = "SELECT * FROM users WHERE age > 20 AND name = 'Rahul'";
$result = mysqli_query($conn, $query);

while ($row = mysqli_fetch_assoc($result)) {
    echo $row['email'];
}
?>

Output:

rahul@example.com

Using WHERE with OR Condition in PHP MySQL

<?php
$query = "SELECT * FROM users WHERE name='Amit' OR name='Neha'";
$result = mysqli_query($conn, $query);

while ($row = mysqli_fetch_assoc($result)) {
    echo $row['name'] . "<br>";
}
?>

Output:

Amit
Neha

Using WHERE with LIKE Operator in PHP MySQL

<?php
$query = "SELECT * FROM users WHERE name LIKE 'R%'";
$result = mysqli_query($conn, $query);

while ($row = mysqli_fetch_assoc($result)) {
    echo $row['name'];
}
?>

Output:

Rahul

WHERE Clause with UPDATE Query in PHP

<?php
$query = "UPDATE users SET age = 27 WHERE name = 'Rahul'";
mysqli_query($conn, $query);

echo "Age updated";
?>

Output:

Age updated

WHERE Clause with DELETE Query in PHP

<?php
$query = "DELETE FROM users WHERE id = 3";
mysqli_query($conn, $query);

echo "Record deleted";
?>

Output:

Record deleted

Secure WHERE Clause Using Prepared Statements

Prepared statements protect against SQL injection.

<?php
$stmt = mysqli_prepare($conn, "SELECT * FROM users WHERE email = ?");
mysqli_stmt_bind_param($stmt, "s", $email);

$email = "rahul@example.com";
mysqli_stmt_execute($stmt);

$result = mysqli_stmt_get_result($stmt);
$row = mysqli_fetch_assoc($result);

echo $row['name'];
?>

Output:

Rahul

Common Mistakes When Using WHERE Clause

Forgetting quotes for string values
Using WHERE without index in large tables
Allowing unchecked user input
Using WHERE incorrectly with AND / OR

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Best Practices for Using WHERE in PHP MySQL

Always validate user input
Use prepared statements
Use indexes on filtered columns
Test conditions before running UPDATE or DELETE
Avoid complex conditions when possible

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Frequently Asked Questions (FAQ)

1. What does WHERE do in MySQL?

It filters records based on conditions.

2. Can WHERE be used with INSERT?

No, WHERE is not used with INSERT.

3. Is WHERE required for UPDATE?

Not required, but strongly recommended.

4. Can I use multiple WHERE conditions?

Yes, using AND / OR.

5. Is prepared WHERE safer?

Yes, it prevents SQL injection.