Sometimes your RDBMS does not allow You certain changes like updating a table without using a WHERE that uses a key column.
When You are really sure what You want to do:
SET SQL_SAFE_UPDATES = 0;
SQL-Basics – Subqueries: Update column with values from another column
Sometimes You screw up your database design and you have redundancies i.e. your database is not normalized. If You want to correct that: Subqueries for the rescue! Continue reading “SQL-Basics – Subqueries: Update column with values from another column”