If you have a table
A (Col1,col2),
a,1
b,1
B (Col1,col2)
a,3
c,2
An inner join is one that returns only data that matches the join condition.
If select * from a join B on a.col1 = B.col1 only returns data that matches the condition a.col1 = b.col1
The results are as follows
a,1,a,3
The left OUTER join not only returns the data that meets the criteria but also returns the data from the left table.
such as SELECT * from a LEFT join B on a.col1 = B.col1 Returns the data that meets the criteria a.col1 = B.col1, and the remainder of a is inconsistent
The corresponding data in B at this time is null
The results are as follows
a,1,a,3
B,1,null,null
The right outer join returns not only the qualifying data but also the data in the right table.
If select * from a RIGHT join B on a.col1 = B.col1 Returns the data that matches the condition a.col1 = B.col1, and the remaining non-conforming data in B, at which point the corresponding data in a is null
The results are as follows
a,1,a,3
null,null,c,2
The difference between SQL leftist right inline
