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 |