A **`JOIN`** clause is used to combine rows from two or more tables based on a related column between them.
A **`self JOIN`** is a regular join, but the table is joined with itself -- this is extremely useful for comparisons within a table.

Joining a table with itself means that each row of the table is combined with itself *and* with every other row of the table.

# Syntax
```sql
SELECT column_names
FROM table1 T1, table1 T2
WHERE condition;
```
Aliases for the actual table names are used to distinguish ​column names from one another since both of the tables have the same name. `T1` and `T2` are aliases for the same table. 

# Example
The following table has been created:

**1. User Info**
| **First Name** |**Last Name** | **City** |
| ---------- | ------------ | ------------ |
| John         | Doe         | Lahore |
| Sam          | Smith        | Karachi
| Shawn         | Magen       | Lahore |
| Homer         | Simpson       | Lahore |
| Bart    | Green     | Karachi |

To match customers that are from the same city, we have used the following SQL query that self joins the table:




SELECT A.City,
       B.name AS FirstName1, 
       A.name AS FirstName2
  FROM user_info A, user_info B
  WHERE A.name <> B.name
  AND A.city = B.city 
  ORDER BY A.city

What is a self join in SQL?

A self JOIN in SQL allows a table to be joined with itself, enabling complex comparisons within the same table.

First Name	Last Name	City
John	Doe	Lahore
Sam	Smith	Karachi
Shawn	Magen	Lahore
Homer	Simpson	Lahore
Bart	Green	Karachi