- MySQL知识库 :: sql
- Introducing SQL Sets
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Summary
Because SQL is based on relational algebra, it should come as no surprise that the standard contains several set-oriented operators. In that spirit, it's time we take a look at the UNION operator.
This article was written by John Paul Ashenfelter and published on August 2, 2001 on ONlamp.com magazine. This link has been provided to help you quickly and easily to find the answers to your questions.