mysql multi-table join query

Create a table needed

- Create t1, t2 Table 
Create Table T1 ( 
	key1 VARCHAR (20 is), 
    V1 int (. 4) 
    ); 
    
## ,, import data stored in the data may not have Chinese characters following the path 
load data local infile 'E: / data /t1.csv ' 
	INTO T1 Table 
    Fields terminated by', ' 
    the ignore Lines. 1; 
    
SELECT * from T1; 
    
Create Table T2 ( 
	key2 VARCHAR (20 is), 
    V2 int (. 4) 
    ); 

Load Data local INFILE' E: / Data / t2.csv ' 
	INTO Table T2 
    Fields terminated by', ' 
    the ignore Lines. 1;

　　- connect the left and right connections and internal connections

## left connecting 

SELECT * from the Join left T1 = T2 ON t1.key1 t2.key2; 

## right connecting 

select * from t1 right join t2 on t1.key = t2.key2; 

connections within ## 

SELECT * from the Join Inner T1 t2.key2 t1.key1 = ON T2; 


## combined query 

SELECT * from T1 
union ## to eliminate duplicate fields with the union not eliminate duplicate fields All union 
SELECT * from T2; 




- Cartesian product: select field 1 [, ... ] from table 1, table 2 [, ...]; 

SELECT * from T1, T2; 


- elimination Cartesian product: select field 1 [, ...] from table 1, table 2 [, ...] where table 1.key = table 2.key; 
SELECT * T1, T2 from 
; WHERE t1.key1 = t2.key2 

SELECT * from the Join cross T1 = T2 ON t1.key1 t2.key2; cross-connect ## 

## Note :: Cartesian product after elimination and the results of the same cross-connect 
 
### in a fully connected mysql no fully connected, but can be combined and right connections to the weight obtained by the left;
SELECT * from the Join left T1 = T2 ON t1.key1 t2.key2 
Union
select * from t1  right join t2  on t1.key = t2.key2;