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How do I represent a subquery in relation algebra? Do I put the new select under the previous select condition?
SELECT number
FROM collection
WHERE number = (SELECT anotherNumber FROM anotherStack);
654
Then you have to convert the sub-query first into relational algebra. To do this for the sub-query given above: PI[some-column-from-sub-query]( SIGMA[extra-where-clause-if-needed ^ some-column = some-column-from-sub-query ](RO[T1](R1) x RO[T2](R2) x ...
In SQL, it's possible to place a SQL query inside another query known as subquery. For example, SELECT * FROM Customers WHERE age = ( SELECT MIN(age) FROM Customers ); Run Code. In a subquery, the outer query's result is dependent on the result-set of the inner subquery.
Subquery must be enclosed in parentheses. Subqueries are on the right side of the comparison operator. ORDER BY command cannot be used in a Subquery. GROUPBY command can be used to perform same function as ORDER BY command.
A subquery is a query that is nested inside a SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery.
You would just rewrite that as a join.
I'm not sure how widely used the syntax I learned for Relational Algebra is so in words.
anotherNumber from anotherStack anotherNumber from the result of step 1 as number
collection
number from the result of step 3
121
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