SQL Joins
SQL join is used to
combine data from two or more tables based on a related column between them.
Joins allow you to retrieve data from multiple tables and combine them into a
single result set.
Then, we can create the following SQL statement (that contains an INNER JOIN), that selects records that have matching values in both tables:
SELECT Orders.OrderID,
Customers.CustomerName,
Orders.OrderDate
FROM OrdersINNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;
There are several types of SQL joins, including:
Inner Join: Retrieves only the matching rows from both tables based on the common column between them.
Syntax:
SELECT column1, column2, ...
FROM table1
JOIN table2
ON table1.common_column = table2.common_column;
Left Join
(or Left Outer Join): Retrieves all the rows from
the left
table (table1), and
the matching rows
from the right table (table2). If
there is
no match in the right table, NULL
values are returned. Syntax:
SELECT column1, column2, ...
FROM table1
LEFT JOIN
table2
ON table1.common_column = table2.common_column;
Right Join
(or Right Outer Join): Retrieves all the rows from the right table (table2), and the matching rows from
the left
table (table1). If
there is
no match in the left table, NULL values are returned. Syntax:
SELECT column1, column2, ...
FROM table1
RIGHT JOIN
table2
ON table1.common_column = table2.common_column;
Full Join (or Full Outer Join): Retrieves all the rows from both tables, including unmatched rows from both tables. If there is no match in either table, NULL values are returned. Syntax:
SELECT column1, column2, ...
FROM table1
FULL JOIN
table2
ON table1.common_column = table2.common_column;
Cross Join: Retrieves the Cartesian product of both tables, i.e., all possible combinations of rows from both tables. Syntax:
SELECT column1, column2, ...
FROM table1
CROSS JOIN table2;
These
are some
of the common types of SQL joins that can be used to combine data from
two or
more tables based on related columns. The appropriate type of join
to use depends on the specific requirements of your query and the relationships between your tables.
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