What is a Join in terms of database

Question

Hi!!

Can someone tell me what exactly does a join mean in terms of databases?

Answer 1

JOINS are used to combine rows from two or more tables, based on a related column between those tables. The following are the types of joins: 

• INNER JOIN: This join returns those records which have matching values in both the tables.
• FULL JOIN: This join returns all those records which either have a match in the left or the right table.
• LEFT JOIN: This join returns records from the left table, and also those records which satisfy the condition from the right table.
• RIGHT JOIN: This join returns records from the right table, and also those records which satisfy the condition from the left table.

Refer to the image below.

INNER JOIN

Syntax:

SELECT column_name(s)
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;

FULL JOIN

Syntax:

SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2 ON table1.column_name = table2.column_name;

LEFT JOIN

Syntax:

SELECT column_name(s)
FROM table1
LEFT JOIN table2 ON table1.column_name = table2.column_name;

RIGHT JOIN

Syntax:

SELECT column_name(s)
FROM table1
RIGHT JOIN table2 ON table1.column_name = table2.column_name;