Query Execution
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Sort -> blocking operator

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PAGES(R) = 1,000

Sort:  M=1,000 blocks for this operation

Cost = 1,000 (Read once + output)

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Sort:  M=500 blocks for this operation

Step 1: Read 500 blocks, sort and write, Read 500 blocks, sort and write
(results in 2 sorted groups)

Cost = 2,000

Step 2: Read one block from each sorted group, merge and output

Cost = 1,000 (Read R once and output)

Total Cost = 3,000

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PAGES(R) = 1,000

Sort: M = 50 blocks

Step 1: Read in 50 blocks at a time, sort and write to temp.

Cost = 2,000  (Read R once + Write R once)

Sorted groups: 1,000/50= 20 sorted groups

Step 2: I need 20 blocks to be able to merge, I have 50!

Read R and merge amd output,

Cost = 1,000

Total cost = 3,000

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Sort: M = 10 blocks

Step 1: Read 10 blocks at a time, sort and write.

Cost = 2,000 (read once write once)

Sorted groups: 100

Step 2: Merge 10 groups at a time and write!

Cost = 2,000 (read once/write once)

Reduce 100 sorted groups -> 10 sorted groups

Step 2: Merge 10 groups and output

Cost = 1,000

Total cost = 5,000

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select
    R.A
    , count(*) as num
from
   R,S
where
   R.A=S.A
group by
   R.A
order by
   R.A, num ;

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