September 2015
Beginner
288 pages
5h 39m
English
Content preview from Oracle PL/SQL in 10 Minutes, Sams Teach Yourself
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Lesson 17. Combining Queries
In this lesson, you’ll learn how to use the UNION operator to combine multiple SELECT statements into one result set.
Understanding Combined Queries
Most SQL queries contain a single SELECT statement that returns data from one or more tables. Oracle also enables you to perform multiple queries (multiple SELECT statements) and return the results as a single query result set. These combined queries are usually known as unions or compound queries.
There are basically two scenarios in which you would use combined queries:
To return similarly structured data from different tables in a single query
To perform multiple ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.