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I think it should be option a)

All query $1,3,4$ are equivalent but $2$ is not equivalent.

Query $2$ should be 

$\prod \text{Room no,hotel no,type,price}(\sigma \text{type='single' } \wedge \text{price=200 })$

1 Answer

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1 votes

When you don't use project and do only select, by default all the columns are returned, thus making Query 2 same as Query 1. 

Eg:

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Online Site For practicing Relational Algebrahttps://dbis-uibk.github.io/relax/calc.htm