What potential issues can arise when using UNION and GROUP in MySQL queries for complex database queries like chat programs?

Using UNION and GROUP in MySQL queries for complex database queries like chat programs can lead to performance issues due to the large amount of data being processed. To optimize these queries, it is recommended to use proper indexing on the columns being queried and limit the amount of data being fetched by using appropriate WHERE clauses. 

// Example of optimizing a query using indexing and WHERE clause
$query = "SELECT * FROM messages WHERE chat_id = :chat_id ORDER BY timestamp DESC LIMIT 10";
$stmt = $pdo->prepare($query);
$stmt->execute(['chat_id' => $chat_id]);
$messages = $stmt->fetchAll();

Keywords

UNION GROUP MySQL queries chat programs database queries

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