Mysql A left(right) join B on A.id=B. ID and a.age=1 and a left (right) join b on a.id=b id where A.age=1

Mysql Of join…on…and… And join…on…where… The difference between

Mysql A left(right) join B on A.id=B.id and A.age=1 And A left(right) join B on A.id=B.id where A.age=1 The difference between

Table building and data preparation

Create left and right tables , And table building statements and data insertion

create table tab_left(
 id int,
 name int,
 age int,
 sex int
);
insert into tab_left values(1,1,1,1),(2,2,2,2),(3,3,3,3),(4,4,4,4),(5,5,5,5),(6,6,6,6);

create table tab_right(
	id int,
	state int,
	money int
);
insert into tab_right values(1,1,1),(2,2,2),(3,3,3),(4,4,4),(7,7,7),(8,8,8);

see tab_left data

select * from tab_left;

See the table tab_right data

select * from tab_right;

Internal connection

There is no difference between the two

adopt id Make internal connections , And specify the left table name Equal to a specific value , Can only get name Records equal to a specific value .

select * from tab_left l join tab_right r on l.id=r.id where l.name=2;

select * from tab_left l join tab_right r on l.id=r.id and l.name=2;

Consistent result

select * from tab_left l join tab_right r on l.id=r.id and r.state=8;

After internal connection ,8 It doesn't contain ,where Filter no records , So for null

Left connection （ The right connection is similar ）

join...on....and... Connect on the left （ The right connection ） eligible Make internal connections , Do not conform to the Make external connections

join...on...where..., Connect outside first , It's filtering

where 1

select * from tab_left l left join tab_right r on l.id=r.id where l.name=2;

Through the first id Make external connections , Re filtration name Records equal to a specific value .

and 1

select * from tab_left l left join tab_right r on l.id=r.id and l.name=2;

If only the left connection is made ,1 To 4 Internal connection should be made ,5 To 6 Make external connections ,

add name The connection condition is amount to Only the qualified ones are internally connected , Others use external connections . Only 2 accord with , Make internal connections

where 2

select * from tab_left l left join tab_right r on l.id=r.id where r.state=3;

Through the first id Make external connections , Re filtration state Records equal to a specific value .

and 2

select * from tab_left l left join tab_right r on l.id=r.id and r.state=3;

If only the left connection is made ,1 To 4 Internal connection should be made ,5 To 6 Make external connections ,

add state The connection condition is amount to Only the qualified ones are internally connected , Others use external connections . Only 3 accord with , Make internal connections

and 3

select * from tab_left l left join tab_right r on l.id=r.id and r.state=8;

If only the left connection is made ,1 To 4 Internal connection should be made ,5 To 6 Make external connections ,

add state The connection condition is amount to Only the qualified ones are internally connected , Others use external connections . There is no such thing as , So all on the right are null.