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Sql Joins



Different SQL JOINs
Before we continue with examples, we will list the types of JOIN you can use, and the differences between them.
· JOIN: Return rows when there is at least one match in both tables
· LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table
· RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table
· FULL JOIN: Return rows when there is a match in one of the tables

The INNER JOIN keyword return rows when there is at least one match in both tables.
SQL INNER JOIN Syntax
SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: INNER JOIN is the same as JOIN.


The INNER JOIN keyword return rows when there is at least one match in both tables. If there are rows in "Persons" that do not have matches in "Orders", those rows will NOT be listed.


The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matches in the right table (table_name2).


SQL LEFT JOIN Syntax
SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: In some databases LEFT JOIN is called LEFT OUTER JOIN.


The LEFT JOIN keyword returns all the rows from the left table (Persons), even if there are no matches in the right table (Orders).


SQL RIGHT JOIN Keyword
The RIGHT JOIN keyword returns all the rows from the right table (table_name2), even if there are no matches in the left table (table_name1).
SQL RIGHT JOIN Syntax
SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: In some databases RIGHT JOIN is called RIGHT OUTER JOIN.


The RIGHT JOIN keyword returns all the rows from the right table (Orders), even if there are no matches in the left table (Persons).



SQL FULL JOIN

The FULL JOIN keyword return rows when there is a match in one of the tables.
SQL FULL JOIN Syntax
SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name=table_name2.column_name



The FULL JOIN keyword returns all the rows from the left table (Persons), and all the rows from the right table (Orders). If there are rows in "Persons" that do not have matches in "Orders", or if there are rows in "Orders" that do not have matches in "Persons", those rows will be listed as well.



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