MySQL distinct

The DISTINCT keyword is typically used with the SELECT statement to ensure that each row in the query result is unique.

Usage with Multiple Columns

The DISTINCT keyword can be used on multiple columns. In this case, only rows where all specified columns are the same will be considered duplicates and removed.

SELECT DISTINCT name, email FROM users;

Considerations

1. Performance: Using the DISTINCT keyword can impact query performance, as MySQL needs to perform additional operations to eliminate duplicate rows. For large datasets, it should be used cautiously and the query performance should be tested.
2. NULL Values: DISTINCT treats NULL values as a unique value. For instance, if a column contains multiple NULL values, DISTINCT will still return one NULL.