For allpages-locked tables where clustered indexes are used
to perform the scans, the search arguments on the index are used
to position the search on the first matching row of each table.
The total cost of the query is the cost of scanning forward on the
data pages of each table. For example, with clustered indexes on* t1(c1)* and *t2(c1)*,
the query on two allpages-locked tables can use a full-merge join:

select t1.c2, t2.c2 from t1, t2 where t1.c1 = t2.c1 and t1.c1 >= 1000 and t1.c1 < 1100

If there are 100 rows that qualify from *t1*,
and 100 rows from *t2*, and each of these tables
has 10 rows per page, and an index height of 3, the costs are:

3 index pages to position the scan on the first matching row of

*t1*Scanning 10 pages of

*t1*3 index pages to position the scan on the first matching row of

*t2*Scanning 10 pages of

*t2*