Comments - User-Defined Variables
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Check the docs for MySQL for more detail. The "order" of @var:=@var+1 is never undefined, as the RHS *must* be evaluated first. The problem is that the order of evaluation of *columns* is undefined, so:
SET @v := 5; SELECT @v, @v:=10;
Might return either [5,10] or [10,10], depending on which column is evaluated first.
"Evaluation of *columns* is undefined". That is that SELECT @v:=5, @v=@v+5 may return [5,10] or [10,5] because the order of columns in SELECT col1, col2 does not follow from left to right? I assume that this is because of sql-philosophy (set theory) since order does not play a role. Is there a way to consider the order?