The MySQL command line client has an argument "--i-am-a-dummy" that refuses to run UPDATE and DELETE's without a WHERE clause.

More commands could use options to adjust how big guns they let you fire at your feet with...

I always SELECT first and confirm I got the right result. Then I add the DELETE just before SELECT and commment out the SELECT line. Never fails!

After doing that on a local db a couple of times, I started just writing the where clause first. Goes like this

WHERE id = 1 ctrl + a DELETE FROM....

Found it's also helpful for writing SELECTS and avoiding the whole "oh crap, now let's load the entire DB" type of moments.

If you're in a GUI where you can run only the highlighted code, I do this:

    select * -- delete
    from sometable
    where id = 1

Then you can run the whole thing to see what would be deleted, and highlight starting at the word delete to actually delete.

Do that once on a production system in the middle of a shipping run. Lesson learned.

All my deletes written first as selects now, as a sibling comment suggested.

That's what transactions are for. you realize the mistake, type ROLLBACK, and move on.

Oh yeah, you're using a toy database aren't you.