How to use SELF JOIN in MySQL?
To use SELF JOIN, let us create a table. The query to create a table is as follows −
mysql> create table SelfJoinDemo
-> (
-> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> CountryName varchar(20),
-> CountryRank int,
-> `Year` varchar(10)
-> );
Query OK, 0 rows affected (1.02 sec)
Now you can insert some records in the table using insert command. The query is as follows −
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('US',1,'2016');
Query OK, 1 row affected (0.12 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('UK',5,'2013');
Query OK, 1 row affected (0.16 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('France',45,'2010');
Query OK, 1 row affected (0.21 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('Turkey',3,'2000');
Query OK, 1 row affected (0.17 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('Japan',78,'1995');
Query OK, 1 row affected (0.21 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('Romania',110,'2007');
Query OK, 1 row affected (0.22 sec)
mysql> insert into SelfJoinDemo(CountryName,CountryRank,`Year`) values('UK',3,'2000');
Query OK, 1 row affected (0.16 sec)Display all records from the table using a select statement. The query is as follows −
mysql> select *from SelfJoinDemo;
The following is the output −
+----+-------------+-------------+------+
| Id | CountryName | CountryRank | Year |
+----+-------------+-------------+------+
| 1 | US | 1 | 2016 |
| 2 | UK | 5 | 2013 |
| 3 | France | 45 | 2010 |
| 4 | Turkey | 3 | 2000 |
| 5 | Japan | 78 | 1995 |
| 6 | Romania | 110 | 2007 |
| 7 | UK | 3 | 2000 |
+----+-------------+-------------+------+
7 rows in set (0.00 sec)
Here is the query of SELF JOIN −
mysql> SELECT DISTINCT t1.CountryName, t2.Year
-> FROM SelfJoinDemo AS t1,
-> SelfJoinDemo AS t2
-> WHERE t1.Year=t2.Year
-> and t1.CountryName='US';
The following is the output −
+-------------+------+
| CountryName | Year |
+-------------+------+
| US | 2016 |
+-------------+------+
1 row in set (0.00 sec
Published on 27-Feb-2019 13:14:01
