代码如下:
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
INNER JOIN table_b B
ON A.PK = B.PK;
查询结果:
代码如下:
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
LEFT JOIN table_b B
ON A.PK = B.PK;
查询结果:
代码如下:
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
RIGHT JOIN table_b B
ON A.PK = B.PK;
查询结果:
代码如下:
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
FULL JOIN table_b B
ON A.PK = B.PK;
上面代码在mysql执行是报错的,因为mysql不支持全连接,只能用以下代码实现效果,含义是左连接+右连接+去重=全。
所谓的去重,实际上就是使用UNION,取并集:
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
LEFT JOIN table_b B
ON A.PK = B.PK
UNION
SELECT A.PK AS A_PK,A.Value AS A_Value,B.PK AS B_PK,B.Value AS B_Value
FROM table_a A
RIGHT JOIN table_b B
ON A.PK = B.PK;
查询结果:
代码如下:
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
LEFT JOIN Table_B B
ON A.PK = B.PK
WHERE B.PK IS NULL
查询结果:
代码如下:
SELECT A.PK AS A_PK, A.Value AS A_Value, B.PK AS B_PK,
B.Value AS B_Value
FROM Table_A A
RIGHT JOIN Table_B B
ON A.PK = B.PK
WHERE A.PK IS NULL
查询结果:
代码如下:
SELECT A.PK AS A_PK, A.Value AS A_Value,
B.Value AS B_Value, B.PK AS B_PK
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.PK = B.PK
WHERE A.PK IS NULL
OR B.PK IS NULL
由于mysql不支持full join,只能通过下面代码模拟实现:
SELECT A.PK AS A_PK, A.Value AS A_Value, B.PK AS B_PK,
B.Value AS B_Value
FROM table_a A
LEFT JOIN table_b B
ON A.PK = B.PK
WHERE B.PK IS NULL
UNION ALL
SELECT *
FROM table_a A
RIGHT JOIN table_b B
ON A.PK = B.PK
WHERE A.PK IS NULL;
查询结果: