Answer:
Since the natural join is based on the column with the same name in both tables, only one copy of the column will be retained in the result, which means that the result will have only one column named "x".
To evaluate the query using a sort-merge join algorithm, both tables must be sorted on the column "x".
Since the memory can hold only 2 pages, we can sort one of the tables in memory, and the other table will have to be sorted on disk. We will choose to sort t2 in memory and t1 on disk.
Sorting t2 in memory requires loading all 10 rows, which occupy 1 page.
Sorting t1 on disk requires at least two passes: one to read the data and sort it, and another to write the sorted data back to disk. In the first pass, we can read 2 pages (half of the available memory) and sort them, so we need to make 2 passes to sort all 20 rows. Therefore, to sort t1, we need to load at least 4 pages (2 passes x 2 pages per pass).
After both tables are sorted, we can merge them using a two-way merge. The merge process requires reading one page of each table at a time and comparing the values of the "x" column. Since t2 occupies only 1 page, we can read all of its data in one pass. However, t1 occupies 4 pages, so we need to make 4 passes to read all of its data.
Therefore, the total number of disk pages that will be loaded to evaluate this query is:
1 page (to sort t2) + 4 pages (to read t1) = 5 pages
Step-by-step explanation:
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