SQL的各种连接（cross join、inner join、full join)的用法理解

#交叉连接CROSS JOIN 又称为笛卡尔积
SELECT student.*,score.* FROM student, score
SELECT student.*,score.* FROM student CROSS JOIN score

#内连接 INNER可省略
SELECT stu.*,score.* FROM student stu,score WHERE
stu.id = score.stu_id

SELECT stu.*,score.* FROM student stu  INNER JOIN score ON
stu.id = score.stu_id

#左外连接 左连接  OUTER可省略
SELECT stu.*,score.* FROM student stu  LEFT  OUTER JOIN score ON
stu.id = score.stu_id

#右外连接 右连接  OUTER可省略
SELECT stu.*,score.* FROM student stu  RIGHT OUTER JOIN score ON
stu.id = score.stu_id

#全外连接  MySQL不支持FULL JOIN
SELECT student.*,score.* FROM student FULL OUTER JOIN score ON student.id = score.stu_id;