How Laravel manages MySQL variables?

Question

If I do

DB::statement("SET @foo := 1;");
DB::select("SELECT @foo;");

I get the expected 1 in the result. But I can't find anywhere whether it is a guaranteed result. If I understand correctly the variables are specific to MySQL connection. So is it possible that those 2 statements will be performed on different connections for some reason and I'll get different result? Can I rely on it to always work?

Answer 1

To ensure both statements are always executed as one single statement you can use database transactions:

DB::transaction(function () {
    DB::statement("SET @foo := 1;");
    DB::select("SELECT @foo;");
});

This guarantees that each transaction is treated as a single "unit" (atomicity). There are two possibilities: both statements are executed as one or if a failure occurs non statement is executed at all.

The next guarantee is: both statements are executed in isolation that means if you execute this code concurrently it is always guaranteed that the transactions were executed sequentially.