理解semi-join in database

• Overview

  semi-join是relational algebra的一种具体形式

• 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.

• References

1. Using Semi-Joins to Solve Relational Queries