1. If you use select * from APowerB without any conditions, the result will be displayed associated with tables an and b, but the result will be repeated many times
2, and select * from a join b, will not add any query conditions, and the result will be the same as 1. Ab is displayed side by side but the result is repeated many times
select * from a:
1 11
2 22
3 33
4 44
5 55
select * from b:
1 a
2 b
3 c
4 d
5 e
6 f
select * from a, B:
1 11 1a
2 22 1 a
3 33 1 a
4 44 1 a
5 55 1 a
1 11 2 b
2 22 2 b
3 33 2 b
4 44 2 b
5 55 2 b
1 11 3 c
2 22 3 c
3 33 3 c
4 44 3 c
5 55 3 c
1 11 4 d
2 22 4 4 4 d
1 11 5 e
2 22 5 e
3 33 5 e
4 44 5 e
5 55 5 e
1 11 6 f
2 22 6 f
3 33 6 f
4 44 6 f
5 55 6 f
Why is this? What is the order of multi-table queries?
what I actually want is
1 11 1a
2 22 2 b
3 33 3 c
4 44 4 d
5 55 5 e
null null 6 f
what should I do? Of course, it"s easy to add conditions directly with rightjoin. But what if there are matching conditions between an and b?