내부 조인

SELECT * FROM A INNER JOIN B ON A.KEY = B.KEY

Select tables A & B and compare key values of table A and table B and return records which only have the identical key values in both tables of A & B. This is similar to the Set theory operation Intersection which is denoted by A ∩ B, the set containing all elements of A that also belong to B.

왼쪽 조인

SELECT * FROM A LEFT JOIN B ON A.KEY = B.KEY

Select tables A & B and compare key values of table A and table B and return all records of A which is in the left side of the sql query but in case of B which is in right side of sql query, only returns records that have the same key values of table A.

오른쪽 조인

SELECT * FROM A RIGHT JOIN B ON A.KEY = B.KEY

Select tables A & B and compare key values of table A and table B and return all records of B which is in the right side of the sql query but in case of A which is in left side of sql query, only returns records that have the same key values of table B.

SELECT * FROM city JOIN country ON city.country_code = country.country_code

SELECT city.name, city_id FROM city JOIN country USING city_id

전체 외부 조인

SELECT * FROM A FULL OUTER JOIN B ON A.KEY = B.KEY

Select tables A & B and compare key values of table A and table B and return all records of both A & B and fill in NULL for missing matches on either side.

왼쪽 외부 조인

SELECT * FROM A LEFT OUTER JOIN B ON A.KEY = B.KEY WHERE B.KEY IS NULL

Left outer join returns set of records from A, with the matching records in B (which are available). If there is no match, the right side will have null.

오른쪽 외부 조인

SELECT * FROM A RIGHT OUTER JOIN B ON A.KEY = B.KEY WHERE A.KEY IS NULL

Right outer join returns set of records from B, with the matching records in A (which are available). If there is no match, the left side will have null.

교차 없는 전체 외부 조인

SELECT * FROM A FULL OUTER JOIN B ON A.KEY = B.KEY WHERE A.KEY IS NULL OR B.KEY IS NULL

Full outer join without intersection returns the set of records only in table A, but not in table B or the set of records only in table B, but not in table A. This clause returns all records that match the ON condition, excluding those are in common between two tables, or those records exist in both tables.