Database Redesign
Before any changes to database structure are attempted one should first:

test any changes on a test database only.
create a complete backup of the operational database only.
clearly understand the current structure and contents of the database only.
All of these

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Database Redesign
Which is not true of a correlated subquery?

They are very similar to a regular subquery.
They can be used to verify functional dependencies.
The processing of the SELECT statements is nested.
EXISTS/NOT EXISTS is a form of a correlated subquery.

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