from the Documentation, this is the sintax of STORE statement:
store[ *fieldlist from] table into filename [ format-spec ];
format-spec ::= ( ( txt | qvd ) )
SO you can use (txt) or (qvd). If format-spec is omitted, (qvd) is used.
So we can assume that if you want store in a qvd, it's the same thing.
1.STORE TAB INTO tab.qvd;
2.STORE TAB INTO tab.qvd(qvd);
both will gave the same result
but in second query u can save like
STORE TAB INTO tab.qvd(txt); it is also gave same result
i.e (QVD)/(txt) in which format u need to save that is ur wish else by default it is saved qvd format
hope i reach clear your doubt 80 % any way u can try once
giving defining file type for QVD is not mandatory because QlikView understand it.
But when your will store into some txt format like CSV you need to give file type.
STORE B into B.qvd;
STORE B into B.qvd(QVD);
Above both statements are same.
but below are different.
if you will use (txt) QV will load correct data but when you will not specify the format it will jot load data correctly it will be considered in xml format.
STORE B into csvB.csv(txt);
STORE B into wthoutcsvB.csv;