Guarded update
An `UPDATE` whose `WHERE` also checks a condition, such as `AND stock >= ?`. It checks and changes the stock in one step, so Kettle & Crane can't oversell the last decaf.
An `UPDATE` whose `WHERE` also checks a condition, such as `AND stock >= ?`. It checks and changes the stock in one step, so Kettle & Crane can't oversell the last decaf.