Should I use on or where for the left join

One 、 Some opinion or conclusion
1、inner join： have left and right The union of the properties of , You need data in both tables to match on Conditions , To be screened out

2、left join： It doesn't care on Is the condition in true , Will return to the records in the table on the left .

3、right join： It doesn't care on Is the condition in true , Will return the records in the table on the right

4、on The condition is the condition used to generate the temporary table ,where The condition is that after the temporary table is generated , Then filter the temporary table .

5、

left join : Left connection , Return all the records in the left table and the records with equal connection fields in the right table .

right join : The right connection , Return all the records in the right table and the records with equal connection fields in the left table .

inner join: Internal connection , It is also called equivalent connection , Return only rows with equal join fields in two tables .

full join: External connection , Returns rows from two tables ：left join + right join.

cross join: The result is Cartesian product , It's the number of rows in the first table multiplied by the number of rows in the second table .

6、

The condition is put directly ON Back , Filter first and then connect ,

Conditional release WHERE Back , Connect first and then filter

 

Two 、 Some references

1、https://www.cnblogs.com/zsq23837880/p/7040923.html

2、https://www.cnblogs.com/dancesir/p/7600265.html