MySQL query, left join (Seek and set), where (seek intersection)

Preparation (two sheet t1,t2):

Table T1:

Mysql> select * from T1;

+-------+---------+

| t1_id | T1_name |

+-------+---------+

| 1 | T1_1 |

| 2 | t1_2 |

+-------+---------+

2 rows in Set (0.02 sec)

Table T2:

Mysql> select * from T2;

+-------+---------+

| t2_id | T2_name |

+-------+---------+

| 2 | t2_2 |

| 3 | T2_3 |

+-------+---------+

2 rows in Set (0.03 sec)

Example of a set:

Mysql> Select T1.t1_id,t2.t2_id,t1.t1_name from T1 left joins T2 on t1.t1_id=t2.t2_id;

+-------+-------+---------+

| t1_id | t2_id | T1_name |

+-------+-------+---------+

| 1 | NULL | T1_1 |

|     2 | 2 | t1_2 |

+-------+-------+---------+

2 rows in Set (0.02 sec)

Intersection instance:

Mysql> Select T1.t1_id,t2.t2_id,t1.t1_name from T1,t2 where t1.t1_id=t2.t2_id;

+-------+-------+---------+

| t1_id | t2_id | T1_name |

+-------+-------+---------+

|     2 | 2 | t1_2 |

+-------+-------+---------+

1 row in Set (0.01 sec)

MySQL query, left join (Seek and set), where (intersection)