Multiple choice

With regard to the expressive power of the former relational query language, which of the following statements is true?

  1. <font size="2">R</font>elational algebra is more powerful than relational calculu<font size="2">s.</font>

  2. <font size="2">R</font>elational algebra has the same power as relational calculu<font size="2">s.</font>

  3. <font size="2">R</font>elational algebra has the same power as safe relational calculus.

  4. <font size="2">N</font>one of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A query can be formulated in relational calculus if and only if it can be formulated in relational algebra. So, relational algebra has the same power as relational calculus.But, it is possible to write syntactically correct relational calculus queries that have infinite number of answers. Such queries are unsafe. Queries that have an finite number of answers are safe relational calculus queries.Thus, Relational algebra has the same power as safe relational calculus. Thus, option (3) is the answer.

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