Questions tagged
join
A JOIN is a general operation in relational algebra for a combining operation on two or more relations in a relational database system. JOIN is also keyword of the SQL language for performing this operation.

An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them. A JOIN is a means for combining fields from two tables (or more) by using values common to each.

ISO/ANSI standard SQL specifies seven types of JOIN:

  • INNER
  • LEFT OUTER
  • RIGHT OUTER
  • FULL OUTER
  • CROSS
  • NATURAL
  • UNION

In SQL, join is used to identify rows from tables that share a common key.

See also A Visual Explanation of SQL Joins.


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left-join inner-join outer-join self-joincross-join full-outer-join right-join natural-join


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