How can the DISTINCT keyword in a MySQL SELECT query be used to prevent duplicate entries in a dropdown list populated from a database in PHP?

When populating a dropdown list from a database in PHP, the DISTINCT keyword in a MySQL SELECT query can be used to prevent duplicate entries from being displayed in the dropdown list. By using DISTINCT, only unique values will be retrieved from the database and displayed in the dropdown list. This ensures that each option in the dropdown list is distinct and eliminates any duplicate entries. 

<?php
// Establish a connection to the database
$connection = mysqli_connect("localhost", "username", "password", "database");

// Query to select distinct values for the dropdown list
$query = "SELECT DISTINCT column_name FROM table_name";

// Execute the query
$result = mysqli_query($connection, $query);

// Populate the dropdown list with distinct values
echo "<select>";
while($row = mysqli_fetch_array($result)) {
    echo "<option value='" . $row['column_name'] . "'>" . $row['column_name'] . "</option>";
}
echo "</select>";

// Close the database connection
mysqli_close($connection);
?>

Keywords

PHP MySQL DISTINCT SELECT query dropdown list

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