Database.SQL.join

Join in SQL

1. SQL Join Types

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1.1 Inner Joins 

Inner joins return rows when the join condition is met.  This is the most common Database join. 

A common scenario is to join the primary key of once table to the foreign key of another.

1.2 Cross Joins

Cross joins return all combinations of rows from each table.  So, if you’re looking to find

all combinations of size and color, you would use a cross join.  

Join conditions aren’t used with cross joins. It pure combinatory joy.

1.3 Outer Joins

Outer joins return all the rows from one table, and if the join condition is met, columns from the other.

They differ from an inner join, since an inner join wouldn’t include the non-matching rows in the final result.

There are three types of outer joins:  Left, Right, and Full outer joins.

1.3.1 Left Outer Join

Left Outer Join – Return all rows from the “left” table, and matching rows from the “right” table. 

If there are no matches in the right table, return Null values for those columns.

1.3.2 Right Outer Join

Right Outer Join – Return all rows from the “right” table, and matching rows from the “left” table. 

If there are no matches in the left table, return Null values for those columns.

1.3.3 Full Join

Full Join – Return all rows from an inner join, when no match is found, return nulls for that table.

该解释需要"推敲"。

2. Inner Join

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Reference

1. inner join 和 outer join的区别

http://en.wikipedia.org/wiki/Join_%28SQL%29

2. Database Joins – Introduction to Join Types and Concepts

https://www.essentialsql.com/introduction-database-joins/

3. SQL Inner Join Tutorial

https://www.essentialsql.com/sql-tutorial/sql-inner-join-tutorial/

4. A SQL join on multiple tables: overview and implementation [To Debug]

https://www.sqlshack.com/different-approaches-to-sql-join-multiple-tables/

https://www.sqlshack.com/sql-multiple-joins-for-beginners-with-examples/

5. How to Join on Multiple Columns

https://learnsql.com/cookbook/how-to-join-on-multiple-columns/

https://learnsql.com/cookbook/

https://learnsql.com/blog/sql-joins-types-explained/

6. What are the different types of SQL JOIN clauses?

https://medium.com/swlh/what-are-the-different-types-of-sql-join-clauses-20f7564b25cb

7. Understanding SQL Joins – All You Need To Know About SQL Joins

https://www.edureka.co/blog/sql-joins-types

8. SQL Joins Explained

http://www.sql-join.com/sql-join-types