How can the issue of duplicate entries in MySQL tables be prevented when using PHP?

Duplicate entries in MySQL tables can be prevented by setting a unique constraint on the columns that should not have duplicate values. This can be done when creating the table or altering it later. When inserting data into the table using PHP, you can catch any potential duplicate entry errors and handle them accordingly, such as displaying an error message to the user or logging the issue for further investigation. 

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

// Set unique constraint on column to prevent duplicate entries
$mysqli->query("ALTER TABLE table_name ADD UNIQUE (column_name)");

// Insert data into table
$query = "INSERT INTO table_name (column1, column2) VALUES (?, ?)";
$stmt = $mysqli->prepare($query);
$stmt->bind_param("ss", $value1, $value2);

$value1 = "value1";
$value2 = "value2";
$stmt->execute();

// Check for duplicate entry error
if ($stmt->errno == 1062) {
    echo "Error: Duplicate entry!";
}

$stmt->close();
$mysqli->close();
?>

Keywords

MySQL PHP duplicate entries prevention database normalization

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