SQL Querying Multiple Tables: Difference between revisions

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=Examples=
All examples provided in this article are based on three tables (<code>person</code>, <code>address</code> and <code>country</code>), with the following schema:
<font size=-2>
<b>person</b>
Column    | Type 
-----------+---------
id        | integer  <font color=teal># primary key</font>
name      | text   
company_id | integer  <font color=teal># foreign key that references company(id)</font>
<b>company</b>
Column    | Type 
-----------+---------
id        | integer <font color=teal># primary key</font>
name      | text   
city_id    | integer <font color=teal># foreign key that references city(id)</font>
<b>city</b>
Column    | Type 
-----------+---------
id        | integer <font color=teal># primary key</font>
name      | text   
</font>




Revision as of 20:24, 23 May 2024

External

Internal

Overview

More than one table can be used in a FROM query clause, and when that happens, it is said that the query performs a join.

Join Condition

If more than one table appears in the FROM clause, then the condition used to link the tables must be included as well. This is the ANSI-approved method. of joining multiple tables, and it is the most portable across various database servers.



Foreign key

Join

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