JOIN

语法说明

JOIN 用于把来自两个或多个表的行结合起来。

下图展示了 LEFT JOIN、RIGHT JOIN、INNER JOIN、和 OUTER JOIN。

• LEFT JOIN

SELECT FROM TableA A LEFT JOIN TableB B ON A.Key=B.Key
SELECT FROM TableA A LEFT JOIN TableB B ON A.Key=B.Key WHERE B.Key IS NULL

• RIGHT JOIN

SELECT FROM TableA A RIGHT JOIN TableB B ON A.Key=B.Key
SELECT FROM TableA A RIGHT JOIN TableB B ON A.Key=B.Key WHERE A.Key IS NULL

• INNER JOIN

SELECT FROM TableA A INNER JOIN TableB B ON A.Key=B.Key

• FULL JOIN

SELECT FROM TableA A FULL OUTER JOIN TableB B ON A.Key=B.Key
SELECT FROM TableA A FULL OUTER JOIN TableB B ON A.Key=B.Key WHERE A.Key IS NULL OR B.Key IS NULL

更多信息，参考：

• LEFT JOIN
• RIGHT JOIN
• INNER JOIN
• FULL JOIN
• OUTER JOIN
• NATURAL JOIN