Visual Explanation of SQL Joins

An SQL join clause combines records from two or more tables in a database. ANSI standard SQL specifies four types of JOINs: INNER, OUTER, LEFT, and RIGHT. Since SQL joins appear to be set-based, its easy to explain using Venn diagrams.

LEFT OUTER JOIN: produces a complete set of records from Table A, with the matching records (where available) in Table B. If there is no match, the right side will contain null.

RIGHT OUTER JOIN: produces a complete set of records from Table B, with the matching records (where available) in Table A. If there is no match, the left side will contain null.

FULL OUTER JOIN: produces the set of all records in Table A and Table B, with matching records from both sides where available. If there is no match, the missing side will contain null.

INNER JOIN: produces only the set of records that match in both Table A and Table B.

8 thoughts on “Visual Explanation of SQL Joins”

  1. Nice post. I learn something more challenging on completely different blogs everyday. It would all the time be stimulating to read content from different writers and practice a little bit something from their store.Thanks for sharing

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