How can a subquery be used in PHP MYSQL to address repeated results in a LEFT JOIN scenario?

When using a LEFT JOIN in MySQL, repeated results can occur if there are multiple matches in the joined table for a single row in the main table. To address this issue, a subquery can be used to group the results from the joined table before joining it with the main table. This ensures that each row from the main table is only matched with a single row from the joined table. 

<?php
// Connect to the database
$mysqli = new mysqli('localhost', 'username', 'password', 'database');

// Query using a subquery to prevent repeated results in LEFT JOIN
$query = "SELECT main_table.*, subquery_table.*
          FROM main_table
          LEFT JOIN (
              SELECT joined_table.*
              FROM joined_table
              GROUP BY joined_table.main_table_id
          ) AS subquery_table
          ON main_table.id = subquery_table.main_table_id";

$result = $mysqli->query($query);

// Fetch and process the results
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        // Process the results
    }
} else {
    echo "No results found.";
}

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

Keywords

subquery PHP MySQL LEFT JOIN repeated results

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