April 2026
Beginner
493 pages
23h 2m
English
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7 Data Query Language
Data query language (DQL) is arguably the most common database feature. We use it to query data from database tables. You’ll learn about data queries from single tables and combined sets of tables, and you’ll also learn about data filters, string and math operations, date- and time-based calculations, and advanced ranking functionalities (window functions). You’ll be able to use this knowledge to query data in your own production databases to generate knowledge.
We’ve finally arrived at the long-awaited chapter on queries! You may presumably be more interested in this chapter than the ones on other SQL sublanguages because data entries are created once, modified when necessary, but queried all the time.
To make a formal ...
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