Nested Loop Join
For each row of the outer input, the inner input is probed once; with an index on the inner join key each probe is a cheap lookup, making nested loops ideal when the outer side is small. Without an index, cost is proportional to outer rows times inner rows, which is why a cardinality underestimate on the outer side is catastrophic here.
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For each row of the outer input, the inner input is probed once; with an index on the inner join key each probe is a cheap lookup, making nested loops ideal when the outer side is small. Without an index, cost is proportional to outer rows times inner rows, which is why a cardinality underestimate on the outer side is catastrophic here.
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