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How to join tables and fetch values from a MySQL database?
To join tables, use the JOIN concept in MySQL. At first, let us create two tables.
Let us create the first table −
mysql> CREATE TABLE `demo52` ( −> `id` INT NOT NULL, −> `name` VARCHAR(20) NOT NULL, −> PRIMARY KEY (`id`) −> ); Query OK, 0 rows affected (1.19 sec)
Insert some records into the table with the help of insert command −
mysql> insert into demo52 values(1,'John'); Query OK, 1 row affected (0.17 sec) mysql> insert into demo52 values(2,'David'); Query OK, 1 row affected (0.10 sec) mysql> insert into demo52 values(3,'Mike'); Query OK, 1 row affected (0.13 sec)
Display records from the table using select statement −
mysql> select *from demo52;
This will produce the following output −
+----+-------+ | id | name | +----+-------+ | 1 | John | | 2 | David | | 3 | Mike | +----+-------+ 3 rows in set (0.00 sec)
Following is the query to create second table.
mysql> CREATE TABLE `demo53` ( −> `id` INT NOT NULL, −> `age` INT NOT NULL, −> PRIMARY KEY (`id`), −> CONSTRAINT `id_demo` FOREIGN KEY (`id`) REFERENCES `demo52` (`id`) −> ); Query OK, 0 rows affected (0.57 sec)
Insert some records into the table with the help of insert command −
mysql> insert into demo53 values(1,23); Query OK, 1 row affected (0.08 sec) mysql> insert into demo53 values(2,22); Query OK, 1 row affected (0.15 sec) mysql> insert into demo53 values(3,26); Query OK, 1 row affected (0.13 sec)
Display records from the table using select statement −
mysql> select *from demo53;
This will produce the following output −
+----+-----+ | id | age | +----+-----+ | 1 | 23 | | 2 | 22 | | 3 | 26 | +----+-----+ 3 rows in set (0.00 sec)
Following is the query to get username by using id −
mysql> SELECT name FROM demo52 t1 −> JOIN demo53 t2 −> ON t1.id=t2.id WHERE t1.id=1;
This will produce the following output −
+------+ | name | +------+ | John | +------+ 1 row in set (0.00 sec)
Updated on: 19-Nov-2020
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