MySQL Database association query "Lert join" common use

One, key words:

1) Left (connection type) join on (condition)

two, common connections:

1) Join (acquisition of a Cartesian product),

SELECT * from T_table1 join T_table2;

2) Left connection (two table associations, after matching criteria, left table remains all, that is, contains no match to the field)

SELECT * from T_table1 LEFT join t_table2 on t_table1.id = t_table2. ID;

3) Right connection (two table associations, after matching criteria, the right table retains all, contains no match to the field)

SELECT * from T_table1 right join t_table2 on t_table1.id = t_table2. ID;

4) Inner connection (get intersection)

SELECT * FROM T_table1 inner join t_table2 on t_table1.id = t_table1. ID;

5) Check only the contents of the left table (two table associations, query the data unique to the left table)

SELECT * from T_table1 left joins t_table2 on t_table1.id = t_table2. ID where t_table2.id is null;

6) Only the right table content (two table association, query the right table unique data)

SELECT * from T_table1 left joins t_table2 on t_table1.id = t_table2. ID where t_table1.id is null;

7) Fully connected

SELECT * from T_table1 LEFT join T_table2 on t_table1. id = t_table2.id

Union

SELECT * from T_table1 right join T_table2 on t_table1. id = t_table2.id;

8) go to the intersection

SELECT * from T_table1 LEFT join t_table2 on t_table1.id = t_table2. ID where t_table2. ID is null

Union

SELECT * from T_table1 right join t_table2 on t_table1.id = t_table2. ID where t_table1. ID is null;

　　

MySQL Database association query "Lert join" common use