A subquery can contain any of the keywords or clauses that an ordinary SELECT query can contain.
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Some advantages of the subqueries:
<ul>
<li \>They allow queries that are structured so that it is possible to isolate each part of a statement.

<li \>They provide alternative ways to perform operations that would otherwise require complex joins and unions.

<li \>They are, in many people's opinion, readable. Indeed, it was the innovation of subqueries that gave people the original idea of calling the early SQL “Structured Query Language.”

</ul>
