First of all the double quotes does not make a difference as to how the column is converted into a field in Qlik. It is only for making sure that if you have special characters in your column name that Qlik is able to delimit the column name.
That is why I prefer to use [ and ] instead of " because it is more obvious that you are quoting a name for an entity like a field name, column name, variable name that has characters in it's name that might confuse Qlik if not quoted. It does not change the values going into the field.
Secondly - if you need to have detailed information about data types for columns in the database source there are three quick table loading shortcuts that can be use in a load script like this:
SQLTables: SQLColumns: SQLTypes:
Yes - exactly like that ... Line #1 will load a table with information of all tables for the current connection (SQL).
Line #2 will give you a table with all the columns and associated information.
Line #3 will give you a table of all the data type information relating to the columns and the tables....
Extremely handy - if you need it - but often overlooked - I think...