🔗 Use SQL triggers to prevent overwriting a value

A trigger lets you run an action when you INSERT, UPDATE or DELETE a value.

Today I wanted to write a value to a SQLite database, and error if the database already had a conflicting value.

There are a variety of ways you could do this – I decided to read the current stored value and check it in Go – but I also discovered there’s a way you could do it in SQL alone using CREATE TRIGGER. I did this with SQLite, but it looks like this is supported by other SQL dialects, including PostgreSQL and MySQL.