How can PHP be used to display values from one table that do not exist in another table in MySQL?

To display values from one table that do not exist in another table in MySQL using PHP, you can use a SQL query with a LEFT JOIN and a WHERE clause to filter out the matching records. By selecting the columns from the first table and checking for NULL values in the columns from the second table, you can retrieve the desired results. 

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT table1.column_name
        FROM table1
        LEFT JOIN table2 ON table1.column_name = table2.column_name
        WHERE table2.column_name IS NULL";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
  // Output data of each row
  while($row = $result->fetch_assoc()) {
    echo "Column Value: " . $row["column_name"] . "<br>";
  }
} else {
  echo "No results found";
}

$conn->close();
?>

Keywords

PHP MySQL SQL query LEFT JOIN data retrieval

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