Why EXISTS a better choice in general than IN?

Answer:

EXISTS informs if a query returned any results as soon as a match is found.E.g.

       SELECT ColumnName(s)

        FROM TABLENAME t1

        WHERE

                -- the statemet turn out true as soon as a match is found

                EXISTS ( SELECT COLUMNNAME(S) 

                        FROM TABLENAME t2

                        WHERE t1.ID = t2.ID

                        )

In comparison, IN compares one value to several values e.g.

        SELECT ColumnName(s)

                FROM TABLENAME t1

                WHERE t1.ID IN(SELECT ID FROM FROM TABLENAME t2)

Also EXISTS clause uses INDEX at the time of fetching records and is there by faster than IN which on the other hand does not.