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What is the cost of joining R and S using a block nested loops join?
Answer: The basic idea of nested-loop join is to do a page-by-page scan of the outer relation, and, for each outer page, do a page-by-page scan of the inner relation. The cost for joining R and S is minimised when the smaller relation S is used as the outer relation. Cost = bS + bS * bR = 200 + 200 * 1000 = 200,200.
When to use block nested loop join?
The block nested-loop join saves major block access in a situation where the buffer size is small enough to hold the entire relation into the memory. It does so by processing the relations on the basis of per block rather on the basis of per tuple.
What is an index nested loop join?
The Nested Loop Join searches for a row in the inner side of the index and seeks the index’s B-tree for the searched value(s) and then stops looking further; it is called an Index Nested Loop Join.
What is nested loop join algorithm?
Nested-Loop Join Algorithm A simple nested-loop join (NLJ) algorithm reads rows from the first table in a loop one at a time, passing each row to a nested loop that processes the next table in the join. This process is repeated as many times as there remain tables to be joined.
How is hash join of two relations R and S computed?
It is the Hash join algorithm in which we have computed the natural join of two given relations r and s. In the algorithm, there are various terms used: tr ⋈ ts: It defines the concatenation of the attributes of tuple tr and ts, which is further followed by projecting out the repeated attributes.
How does a nested loop join work?
A Nested Loops join works in the same way. One of the joining tables is designated as the outer table and another one as the inner table. For each row of the outer table, all the rows from the inner table are matched one by one if the row matches it is included in the result-set otherwise it is ignored.