SQL JOINS

The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables.

Tables in a database are often related to each other with keys.

A primary key is a column (or a combination of columns) with a unique value for each row. Each primary key value must be unique within the table. The purpose is to bind data together, across tables, without repeating all of the data in every table.

SQL INNER JOIN Keyword
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


SQL LEFT JOIN Keyword
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


SQL RIGHT JOIN Keyword
The RIGHT JOIN keyword returns all 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


SQL FULL JOIN Keyword
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