What are the potential pitfalls of using DISTINCT or GROUP BY in PHP when querying a database for unique values?

Using DISTINCT or GROUP BY in PHP when querying a database for unique values can potentially lead to slower query performance, especially when dealing with large datasets. It is important to carefully consider the impact on performance before using these clauses. To optimize the query, you can use the SQL SELECT DISTINCT statement in combination with an appropriate index on the column you want to retrieve unique values from.

// Example of using SELECT DISTINCT with an index
$query = "SELECT DISTINCT column_name FROM table_name";
$result = mysqli_query($connection, $query);

// Ensure an index is set on the column_name for better performance
// CREATE INDEX index_name ON table_name (column_name);