MySQL Connection table Query

Tag: connection where SQL join Select also returns NULL for outer JOIN

SELECT * from test1 a,test2 b where a.no=b.no;; Internal connection

SELECT * FROM Test1 a ieft join test2 B on a.id=b.id; left outer connection

SELECT * from Test1 a right joins Test2 B on A.id=b.id; left outer join (the difference between the left connection is to the left of the main table, will be left null also output, right connection opposite)

The difference between an inner join and an outer join is that the inner join matches only the qualifying item, and the outer join IS null and returns

　

MySQL Connection table Query