本文主要是介绍理解semi-join in database，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
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Overview
semi-join是relational algebra的一种具体形式
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Relational Algebra
In database theory, relational algebra is a theory that uses algebraic structures with a well-founded semantics for modeling data, and defining queries on it.
The theory has been introduced by Edgar F. Codd.
The main application of relational algebra is to provide a theoretical foundation for relational databases, particularly query language for such databases, chief among which is SQL.
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References
- Using Semi-Joins to Solve Relational Queries
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