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Doubt in understanding about NON-UNIQUE INDEX

If I have a table t1 with a column a as follows

A
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2

if i create a non unique index on column A of table t1
and access a row by giving the following select statement
select a from t1 where a > 1;

where we get all the values that are '2' returning 10 rows.

Here the non-unique index goes with index range scan.

1) Is it that it also takes the rowid into account while accessing the row values of 2 ? Are the non-unique index values are unique ?


2) Suppose if i want a particular row value from a particular position say for example 12th position in the column A. How can non-unique index will be useful and how it actually accesses and what will be the query?


3) When and where the non-unique indexes are mainly used ?
Aug 22 '07 #1
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