Question
What is a find duplicates query?
Step 1
It is designed to search for and return any rows that have identical values in one or more columns. The query typically involves comparing the values in specific columns of a table and identifying any instances where the values are the same. This can be useful in Show more…
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Key Concepts
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What is a segmental duplication?
Consider the following SQL query $\begin{array}{lll}\text { SELECT } & \text { DISTINCT } & a_{1}, a_{2}, a_{3} \ldots a_{n}\end{array}$ $R_{1}, R_{2} \ldots R_{m}$ ROM WHERE $\quad P$ For any arbitrary predicate $P$, this query is equivalent to which relational algebra expression? (A) $\Pi_{a_{1}, a_{2}, \ldots a_{n}}\left(\sigma_{p} R_{1} \times R_{2} \times \ldots \times R_{m}\right)$ (B) $\sigma_{a_{1}, a_{2}, \ldots a_{n}}\left(\sigma_{p} R_{1} \times R_{2} \times \ldots \times R_{m}\right)$ (C) $\sigma_{a_{1}, a_{2}, \ldots a_{n}}\left(\prod_{p} R_{1} \times R_{2} \times \ldots \times R_{m}\right)$ (D) $\Pi_{R_{1}, R_{2}, \ldots R_{m}}\left(\sigma_{p} a_{1} \times a_{2} \times \ldots \times\left(a_{n}\right)\right.$
Databases
ER Model and Relational Model
Consider the following query select distinct $a_{1}, a_{2}, \ldots a_{n}$ from $r_{1}, r_{2} \ldots r_{m}$ where $P$ for an arbitrary predicate $P$, this query is equivalent to which of the following relational algebra expressions: (A) $\pi \underset{a_{1} \ldots a_{n}} \sigma_{p}\left(r_{1} \times r_{2} \times \ldots \times r_{m}\right)$ (B) $\pi \underset{a_{1} \ldots a_{n}} \sigma_{p}\left(r_{1} \times r_{2} \times r_{3} \times \ldots \times r_{m}\right)$ (C) $\underset{a_{1} \ldots a_{n}}{\sigma} \pi_{p}\left(r_{1} \times r_{2} \times \ldots \times r_{m}\right)$ (D) $\underset{a_{1} \ldots a_{n}}{\sigma} \pi_{p}\left(r_{1} \times r_{2} \times \ldots \times r_{m}\right)$
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