Joins understanding

There are four basic types of SQL joins: inner, left, right, and full.

  • (INNER) JOIN: Select all records from Table A and Table B, where the join condition is met.

  • LEFT (OUTER) JOIN: Select all records from Table A, along with records from Table B for which the join condition is met (if at all).

  • RIGHT (OUTER) JOIN: Select all records from Table B, along with records from Table A for which the join condition is met (if at all).

  • FULL (OUTER) JOIN: Select all records from Table A and Table B, regardless of whether the join condition is met or not.

The easiest and most intuitive way to explain the difference between these four types is by using a Venn diagram, which shows all possible logical relations between data sets.

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