Imagine in your MySQL database you have a table A like this:
| id |
|---|
| 1 |
| 2 |
| 3 |
| 4 |
and a table B like this:
| id |
|---|
| 1 |
| 2 |
| 5 |
| 6 |
Answer the following questions:
- What would be the result of the following query?
SELECT A.id, B.id FROM A LEFT JOIN B ON A.id=B.id ORDER BY A.id;
a) The syntax is incorrect it produces an error
b) The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 2 | 2 |
| NULL | 5 |
| NULL | 6 |
c) The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | NULL |
| 4 | NULL |
d) The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | NULL |
| 4 | NULL |
| NULL | 5 |
| NULL | 6 |
2) What would be the results of the following query (note the ON condition!)?
SELECT A.id, B.id FROM A LEFT JOIN B ON A.id=A.id ORDER BY A.id;
a) The syntax is incorrect it produces an error
b)The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 1 | 2 |
| 1 | 5 |
| 1 | 6 |
| 2 | 1 |
| 2 | 2 |
| 2 | 5 |
| 2 | 6 |
| 3 | 1 |
| 3 | 2 |
| 3 | 5 |
| 3 | 6 |
| 4 | 1 |
| 4 | 2 |
| 4 | 5 |
| 4 | 6 |
c) The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | NULL |
| 4 | NULL |
d)The table:
| A.id | B.id |
|---|---|
| 1 | 1 |
| 1 | NULL |
| 1 | NULL |
| 1 | NULL |
| 2 | NULL |
| 2 | 2 |
| 2 | NULL |
| 2 | NULL |
| 3 | NULL |
| 3 | NULL |
| 3 | 5 |
| 3 | NULL |
| 4 | NULL |
| 4 | NULL |
| 4 | NULL |
| 4 | 6 |