How to improve the performance of the query?

Is it adviceable to keep all the columns in a table present in Oracle database as primary key or only putting index to the columns which are being used in query without any primary key?

• A table present in Oracle database which will be having information about flights. According to the functionality of the table, only possibility of having primary key is by keeping all the columns as a primary key. Because it may contain duplicate values in all the columns except any one column in a given time which may vary for different records. The table is having 10 columns. Which will improve the performance, either keeping all the columns as primary key or keeping index for the columns used in query without having any primary key...

• Answer:

  You should always have a primary key in a table. In that case, I would never use 10 columns, but instead use an integer field with automatic numbering. To do that in Oracle, use either a trigger or a sequence which will automatically populate the primary key. See Oracle documentation: http://www.orafaq.com/wiki/AutoNumber_and_Identity_columns You probably should also create an index on the table to increase performance.