Question : Oracle Query Tuning

If in a table, a column already has unique index or it has a primary key.
If I create an index on top of this, Will this be worth?

If a table has  table-level primary key, composed of two columns.
and if I create an index on only one column, what will be the impact?
Will there be any performance issues

Answer : Oracle Query Tuning

Dear Sakthi,

There is no rule of thumb in database performance tuning.  See this

Table1(col1,col2,col3) primary key(col1,col2)
Note behavior of each query listed below

sql>select * from table1 where col1=1 and col2=1
will may use primary key index(Index scan)

sql>select * from table1 where col1=1
will may use primary key index(Index scan)

sql>select * from table1 where col2=1
will may use primary key index (index Skip scan, but again this is depend)

To feel this create table with primary key and examine execution plan for different query.