1.from A inner join B on A.ID=B.ID :两表都有的记录才列出
A表： ID Name B表： ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz 4 Null
3 Null Null C4
select * from A inner join B on A.ID=B.ID:
ID Name ID Class
1 BMW 1 C1
2 Aodi 2 C2
SELECT * FROM Table1 t1 INNER JOIN Table2 t2 ON t1.Col1 = t2.Col1
2.from A left join B on A.ID=B.ID:
A表中所有记录列出，B中无法匹配的用Null匹配
A表： ID Name B表： ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz 4 Null
3 Null Null C4
select * from A left join B on A.ID=B.ID:
ID Name ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz Null Null
3 Null Null Null
SELECT * FROM Tables1 t1 LEFT OUTER JOIN Table2 t2 on t1.Col1 = t2.Col2
SELECT * FROM Table1 t1 LEFT OUTER JOIN Table2 t2 ON t1.Col1 = t2.Col1 WHERE t2.Col1 IS NULL
3.from A right join B on A.ID=B.ID:
B表中所有记录列出,A中无法匹配的用Null匹配
A表： ID Name B表： ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz 4 Null
3 Null Null C4
select * from A right join B on A.ID=B.ID:
ID Name ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Null 4 Null
Null Null Null C4
SELECT * FROM Tables1 t1 RIGHT OUTER JOIN Table2 t2 on t1.Col1 = t2.Col2
SELECT * FROM Table1 t1 RIGHT OUTER JOIN Table2 t2 ON t1.Col1 = t2.Col1 WHERE t2.Col1 IS NULL
4.from A full outer join B on A.ID=B.ID.
列出A表所有记录，B表所有记录。无法匹配的用Null替代
A表： ID Name B表： ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz 4 Null
3 Null Null C4
select * from A full outer join B on A.ID=B.ID.
ID Name ID Class
1 BMW 1 C1
2 Aodi 2 C2
Null Benz Null Null
3 Null Null Null
Null Null 4 Null
Null Null Null C4
SELECT * FROM Table1 t1 FULL OUTER JOIN Table2 t2 ON t1.Col1 = t2.Col1
SELECT * FROM Table1 t1 FULL OUTER JOIN Table2 t2 ON t1.ID = t2.ID WHERE t1.ID IS NULL OR t2.ID IS NULL
CROSS JOIN：
交叉连接不需要任何连接条件。这个会把两个表的的数据进行笛卡尔积操作。
SELECT * FROM Table1 t1 CROSS JOIN Table2 t2