Questions tagged [join]

An SQL JOIN returns rows combined from two tables and possibly satisfying a condition.

ISO/ANSI standard SQL specifies numerous JOINs.

Unconditional/Cross joins:

• CROSS JOIN
• comma (implicit join)

Comma returns a CROSS JOIN but has lower precedence than the keyword joins.

Conditional joins:

• INNER JOIN
• LEFT OUTER JOIN
• RIGHT OUTER JOIN
• FULL OUTER JOIN

Each of those has an ON version, a USING version and a NATURAL version. OUTER is an optional keyword with no effect.

CROSS JOIN returns the rows that can be made by combining a row from the left table with a row from the right table. INNER JOIN ON/USING does a CROSS JOIN then keeps only rows satisfying a condition. LEFT/RIGHT/FULL OUTER JOIN ON/USING does an INNER JOIN then via UNION ALL adds the rows got by NULL-extending the rows from the LEFT/RIGHT/both input tables that did not form an INNER JOIN row.

Specific join tags:

You can specify your question by adding extra tags:

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

Questions:

• Join vs. sub-query
• What is the difference between "INNER JOIN" and "OUTER JOIN"?
• Difference between JOIN and INNER JOIN
• https://stackoverflow.com/questions/448023/what-is-the-difference-between-left-right-outer-and-inner-joins
• SQL JOIN - WHERE clause vs. ON clause