In relational databases, data stored in multiple tables are connected to one another with a common key value. This connection is established by a foreign key inside of the child table linking to the parent. There is a continuous demand to pull the records from connected tables to obtain the complete picture of the data stored in the database.This data is combined using SQL’s JOIN clause, which is part of Data Query Language (DQL), by applying specific conditions.The JOIN clause allows for merging data from multiple tables based on their logical relationships, producing a unified output in the form of a single table.
An INNER JOIN retrieves rows from both tables where there is a matching value in the specified columns. Any rows in “Table1” that do not have a corresponding match in “Table2” will be excluded from the results.
Syntax INNER JOIN
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
A LEFT JOIN retrieves all records from the left table and includes any matching records from the right table that meet the specified condition.
Syntax LEFT JOIN:
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
A RIGHT JOIN retrieves all records from the right table and includes any matching records from the left table that satisfy the specified condition.
Syntax RIGHT JOIN
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;
