SQL LEFT JOIN
The LEFT JOIN returns all rows from the table A, whether or not there is a match with table B.
SQL Left Join syntax
SELECT column_name(s)
FROM A_table LEFT JOIN B_table
ON A_table.column_name = B_table.column_name;
Training_Course
| ID | NAME | DURATION | PRICE |
|---|
| 1 | SQL | 5 | 200 |
| 2 | T-SQL | 7 | 700 |
| 3 | MySQL | 5 | 600 |
| 4 | PL/SQL | 7 | 800 |
| 5 | PostgreSQL | 6 | 500 |
Certifications
| ID | NAME | PRICE | ID_TC |
|---|
| 1 | PostgreSQL certification | 800 | 5 |
| 2 | SQL certification | 350 | 1 |
| 3 | T-SQL certification | 1000 | 2 |
Example
SELECT t.ID,t.NAME,t.PRICE
FROM Training_Course t LEFT JOIN Certifications c
ON t.ID = c.ID_TC ;
Results
| ID | NAME | PRICE |
|---|
| 1 | SQL | 200 |
| 2 | T-SQL | 700 |
| 3 | MySQL | 600 |
| 4 | PL/SQL | 800 |
| 5 | PostgreSQL | 500 |
