sql left join

MySQL [dbi_seminar]> SELECT * FROM seminar LEFT JOIN leiter ON datum='2015-04-30' AND leiter=leiter.id GROUP BY leiter;
+----+------+------------+------+-------+--------+------+------+
| id | name | datum      | raum | thema | leiter | id   | name |
+----+------+------------+------+-------+--------+------+------+
| 38 | S37  | 2015-04-30 |    9 |     3 |      1 |    1 | A0   |
|  1 | S00  | 2015-04-30 |    3 |     2 |      2 |    2 | A1   |
| 14 | S13  | 2015-04-30 |   13 |     3 |      3 |    3 | A2   |
| 24 | S23  | 2015-04-30 |   19 |     1 |      4 |    4 | A3   |
|  7 | S06  | 2015-04-30 |   17 |     1 |      5 |    5 | B0   |
|  4 | S03  | 2015-04-30 |   10 |     3 |      6 |    6 | B1   |
|  2 | S01  | 2015-04-30 |   15 |     3 |      7 |    7 | B2   |
| 21 | S20  | 2015-04-30 |   16 |     2 |      8 |    8 | B3   |
|  3 | S02  | 2015-04-30 |    8 |     2 |      9 |    9 | C0   |
+----+------+------------+------+-------+--------+------+------+
9 ROWS IN SET (0.00 sec)

MySQL [dbi_seminar]> SELECT * FROM seminar JOIN leiter ON datum='2015-04-30' AND leiter=leiter.id GROUP BY leiter;
+----+------+------------+------+-------+--------+----+------+
| id | name | datum      | raum | thema | leiter | id | name |
+----+------+------------+------+-------+--------+----+------+
| 38 | S37  | 2015-04-30 |    9 |     3 |      1 |  1 | A0   |
|  1 | S00  | 2015-04-30 |    3 |     2 |      2 |  2 | A1   |
| 14 | S13  | 2015-04-30 |   13 |     3 |      3 |  3 | A2   |
| 24 | S23  | 2015-04-30 |   19 |     1 |      4 |  4 | A3   |
|  7 | S06  | 2015-04-30 |   17 |     1 |      5 |  5 | B0   |
|  4 | S03  | 2015-04-30 |   10 |     3 |      6 |  6 | B1   |
|  2 | S01  | 2015-04-30 |   15 |     3 |      7 |  7 | B2   |
| 21 | S20  | 2015-04-30 |   16 |     2 |      8 |  8 | B3   |
|  3 | S02  | 2015-04-30 |    8 |     2 |      9 |  9 | C0   |
+----+------+------------+------+-------+--------+----+------+
9 ROWS IN SET (0.00 sec)