thanks for the answer.

>>So is that 13M values with one row each and 1 value with 4M rows?
>>Or is it 9M values with 1 row each and 4M values with 2 rows each?

its the second scenario. most values have 1 row, some values have a low
number of rows, less than 10 is the norm.

>>That would depend on the query

I am using a very simply query.

SELECT * FROM TABLE WHERE X = value;

X is the field indexed, VARCHAR2(9). my test query returns 4 rows