What does SELECT MIN(+ - Column) do?
MIN(+ - schema_id) is parsed as MIN( + (- schema_id) ) which is the same as MIN(- schema_id), so it's (mathematicaly)* the same as -MAX(schema_id). Likewise for the MAX.



*: There are some edge cases when the MIN/MAX(-x) might raise an error while the - MAX/MIN(x) will not (because the negation is applied in all values of the column vs only to the MAX/MIN value).