Microsoft SQL Server Outer Join


Example

Left Outer Join

LEFT JOIN returns all rows from the left table, matched to rows from the right table where the ON clause conditions are met. Rows in which the ON clause is not met have NULL in all of the right table's columns. The syntax of a LEFT JOIN is:

SELECT * FROM table_1 AS t1
LEFT JOIN table_2 AS t2 ON t1.ID_Column = t2.ID_Column 

Right Outer Join

RIGHT JOIN returns all rows from the right table, matched to rows from the left table where the ON clause conditions are met. Rows in which the ON clause is not met have NULL in all of the left table's columns. The syntax of a RIGHT JOIN is:

SELECT * FROM table_1 AS t1
RIGHT JOIN table_2 AS t2 ON t1.ID_Column = t2.ID_Column 

Full Outer Join

FULL JOIN combines LEFT JOIN and RIGHT JOIN. All rows are returned from both tables, regardless of whether the conditions in the ON clause are met. Rows that do not satisfy the ON clause are returned with NULL in all of the opposite table's columns (that is, for a row in the left table, all columns in the right table will contain NULL, and vice versa). The syntax of a FULL JOIN is:

SELECT * FROM table_1 AS t1
FULL JOIN table_2 AS t2 ON t1.ID_Column = t2.ID_Column  

Examples

/* Sample test data. */
DECLARE @Animal table (
    AnimalId Int IDENTITY,
    Animal Varchar(20)
);

DECLARE @AnimalSound table (
    AnimalSoundId Int IDENTITY,
    AnimalId Int,
    Sound Varchar(20)
);

INSERT INTO @Animal (Animal) VALUES ('Dog');
INSERT INTO @Animal (Animal) VALUES ('Cat');
INSERT INTO @Animal (Animal) VALUES ('Elephant');
INSERT INTO @Animal (Animal) VALUES ('Frog');

INSERT INTO @AnimalSound (AnimalId, Sound) VALUES (1, 'Barks');
INSERT INTO @AnimalSound (AnimalId, Sound) VALUES (2, 'Meows');
INSERT INTO @AnimalSound (AnimalId, Sound) VALUES (3, 'Trumpet');
INSERT INTO @AnimalSound (AnimalId, Sound) VALUES (5, 'Roars');
/* Sample data prepared. */

LEFT OUTER JOIN

SELECT * 
FROM @Animal As t1 
LEFT JOIN @AnimalSound As t2 ON t1.AnimalId = t2.AnimalId;

Results for LEFT JOIN

AnimalId    Animal               AnimalSoundId AnimalId    Sound
----------- -------------------- ------------- ----------- --------------------
1           Dog                  1             1           Barks
2           Cat                  2             2           Meows
3           Elephant             3             3           Trumpet
4           Frog                 NULL          NULL        NULL

RIGHT OUTER JOIN

SELECT * 
FROM @Animal As t1 
RIGHT JOIN @AnimalSound As t2 ON t1.AnimalId = t2.AnimalId;

Results for RIGHT JOIN

AnimalId    Animal               AnimalSoundId AnimalId    Sound
----------- -------------------- ------------- ----------- --------------------
1           Dog                  1             1           Barks
2           Cat                  2             2           Meows
3           Elephant             3             3           Trumpet
NULL        NULL                 4             5           Roars

FULL OUTER JOIN

SELECT * 
FROM @Animal As t1 
FULL JOIN @AnimalSound As t2 ON t1.AnimalId = t2.AnimalId;

Results for FULL JOIN

AnimalId    Animal               AnimalSoundId AnimalId    Sound
----------- -------------------- ------------- ----------- --------------------
1           Dog                  1             1           Barks
2           Cat                  2             2           Meows
3           Elephant             3             3           Trumpet
4           Frog                 NULL          NULL        NULL
NULL        NULL                 4             5           Roars