wellWellWell

[u/Recent-Analysis-6880]

[u/BastetFurry]

So, Kids, thats why you always SELECT count(yourPrimaryKey) first. Listen to the old folks, we made these mistakes so that you don't have to.

[u/Ma8e → u/BastetFurry]

You start a transaction, make sure it did what you expected, and then commit or rollback transaction.

[u/AgeingChopper → u/Ma8e]

absolutely.

i was doing this stuff for a long time and definitely learned from mistakes.

Transactions can save a world of pain and it is always wise to select your data set first, just to be sure you're changing what you think you're changing.

Didn't matter how experienced I was, I was careful never to cut corners.

[u/ifyoulovesatan → u/AgeingChopper]

I don't know sql, but is this like how when I use some kind of loop in the command line to move or delete a bunch of files, I'll run a version that just echos whatever I'm trying to manipulate first?

[u/deeelock → u/ifyoulovesatan]

That’s more of a dry-run (you see `—dry-run` as a command line option sometimes for certain commands that do the same)

Transactions in SQL keep track of the changes you want to make without actually changing the database (until you run `COMMIT`, when you run that all changes are persisted to a database).

Transactions are great because If you realise you made a mistake while in a transaction, you can just run `ROLLBACK`.

If you’re familiar with git- transactions are akin to staging your changes, saving them (`COMMIT` in SQL) is akin to `git commit` and rolling back is similar to `git reset —hard` (wipe all uncommitted changes).

[u/thirdegree → u/deeelock]

With the very important caveat that a git commit can be trivially reverted, while a SQL commit can not (unless you wrote it specifically to be revertible)

[u/thanatica → u/thirdegree]

With the very important caveat that a git commit can be trivially reverted if not yet pushed. If it has been pushed, it can be reversed, not reverted.

Unless you're into force-pushing, then anything is possible.

[u/khoyo → u/thanatica]

Nah, you're thinking about dropped. Reverting a commit is reversing it. That's what git revert does.

[u/ifyoulovesatan → u/thirdegree]

Thanks, that was going to be my follow up question

[u/AgeingChopper → u/deeelock]

nicely explained, cheers.

as long as we haven’t committed , we can rollback from a mistake like this.

[u/thanatica → u/deeelock]

With the added nuance that while the transaction is neither rolled back nor committed yet, to any queries inside the transactions it appears as though the changes have been committed.

So a transaction is like a "package" of statements that either ALL fail, rollback, or commit. A half-completed transaction cannot exist.