MySQL Update Queries: Overwriting Existing Values

In MySQL, when updating a table, it's possible to encounter a scenario where the new value you specify for a column is the same as its current value. In such cases, a natural question arises: will MySQL overwrite the existing value or ignore the update altogether?

The MySQL documentation for the UPDATE statement provides the answer:

If you set a column to the value it currently has, MySQL notices this and does not update it.

This means that when you run an update query like:

UPDATE `user` SET user_name = 'John' WHERE user_id = 1

where the column value is already 'John', MySQL will recognize that the new value is identical to the existing one and won't attempt to update it. This is an optimization feature that helps prevent unnecessary database writes.

Therefore, in the example provided, MySQL will not overwrite the existing value and will leave the 'user_name' column unchanged for the user with user_id = 1. This behavior ensures that the database is not unnecessarily burdened with redundant write operations.