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JOIN
It displays data from two or more tables which are in relation. As a result of query
there are returned records which are fitted in both tables.
Syntax
SELECT `column_name1`,`column_name2`
FROM `table_name1`
INNER JOIN `column_name2`
ON `table_name1`.`column_name1`=`table_name2`.`column_name2`
Example
Dispaly name and surname of people from `osoby` table order value from
`orders` table but only those people who has placed any order.
| id | name | surname | age |
|---|
| 1 | Paweł | Kowalski | 3 |
| 2 | Piotr | Janik | 7 |
| 3 | Michał | Nowak | 13 |
| id | order_value | person_id |
|---|
| 1 | 100 | 1 |
| 2 | 200 | 2 |
| 3 | 100 | 2 |
query
SELECT * FROM `people`
INNER JOIN `orders`
ON `orders`.`person_id`=`people`.`id`
result
| id | name | surname | age | id | order_value | person_id |
|---|
| 1 | Paweł | Kowalski | 3 | 1 | 100 | 1 |
| 2 | Piotr | Janik | 7 | 2 | 200 | 2 |
| 2 | Piotr | Janik | 7 | 3 | 100 | 2 |
This same result without JOIN :
SELECT *
FROM `people`,`orders`
WHERE `orders`.`person_id`=`people`.`id`
