This advanced SQL exercise is part of the book: Advanced SQL – Practical Techniques and Use-Cases, which includes 100 day-to-day SQL challenges (and solutions), need-to-know advanced features, and key concepts.

This exercise requires performing the opposite operation compared with the previous question. The “Northern Wind” travel store manages a table that holds the addresses of its customers. You can see that each row indicates the state, city, and address of each customer. In the State and City columns, when a certain value repeats itself, it is replaced with NULL:

CREATE TABLE customerLocations
(c_city varchar(25),
c_state varchar(25),
c_address varchar(50))

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