Consider the following SQL query.
select distinct a1, a2, ..., an
from r1, r2, ..., rm
where P
For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions?
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$\Pi_{a_1, a_2, … a_n} \sigma_p \left(r_1 \times r_2 \times \dots \times r_m\right)$
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$\Pi_{a_1, a_2, … a_n} \sigma_p \left(r_1 \bowtie r_2 \bowtie \dots \bowtie r_m \right)$
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$\Pi_{a_1, a_2, … a_n} \sigma_p \left(r_1 \cup r_2 \cup \dots \cup r_m \right)$
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$\Pi_{a_1, a_2, … a_n} \sigma_p \left(r_1 \cap r_2 \cap \dots \cap r_m \right)$
