Fix incorrect column names for string literals without alias

[JanJakes]

It turns out that when selecting a string literal, the resulting column name differs between MySQL and SQLite.

For example, with a query such as SELECT 'abc':

• In MySQL, the returned column name is abc (the unquoted string value).
• In SQLite, the returned column name is 'abc' (the quoted string).

To address that, we need to use "SELECT 'abc' AS `abc`" in these cases.

[adamziel]

Oh wow, this is such a good find.