General performance recommendations for queries

To obtain maximum performance one should take into consideration following items:

• Don't use empty filters or other queries like 'give me all'. Instead try to construct the filter as strict as possible.
• Try to query as few columns to retrieve as possible. Extra columns to retrieve typically result into joining extra tables, and it is very bad for performance. Also larger set of columns more likely prevents DBMS from using indexes.
• Use sorting only if you really need it. Often proper filtering suits better than sorting.