What are some best practices for outputting data from a relational database in PHP to avoid duplicate entries?

One way to avoid duplicate entries when outputting data from a relational database in PHP is to use the DISTINCT keyword in your SQL query. This will ensure that only unique rows are returned. Another approach is to use GROUP BY to group similar rows together and avoid redundancy. Additionally, you can utilize PHP arrays to store and check for duplicates before displaying the data. 

// Example using DISTINCT keyword in SQL query
$sql = "SELECT DISTINCT column_name FROM table_name";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo $row["column_name"] . "<br>";
    }
}

// Example using GROUP BY in SQL query
$sql = "SELECT column_name FROM table_name GROUP BY column_name";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo $row["column_name"] . "<br>";
    }
}

// Example using PHP arrays to avoid duplicates
$sql = "SELECT column_name FROM table_name";
$result = $conn->query($sql);

$data = array();
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        if (!in_array($row["column_name"], $data)) {
            $data[] = $row["column_name"];
            echo $row["column_name"] . "<br>";
        }
    }
}

Keywords

SQL PHP relational database duplicate entries data output

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