mysql加入逻辑运算符

Question

我只想用JOIN做逻辑运算，得到选中表的所有行。

例如:

任务表:

+------+-------------+-----------+
| id   | name        | projectID |
+------+-------------+-----------+
| 1    | steal       | 3         |
| 2    | sell        | 2         |
| 3    | earn        | 1         |
+------+-------------+-----------+

项目表:

+------+-------------+-----------+
| id   | name        | online    |
+------+-------------+-----------+
| 1    | stealing    | 1         |
| 2    | selling     | 1         |
| 3    | earning     | 0         |
+------+-------------+-----------+

选择项目在线的所有任务(online = 1)

我尝试过的:

SELECT * 
FROM  `task` 
LEFT JOIN  `project` ON project.id = task.projectID && project.online =1

这导致项目和任务的所有行但是我只想要任务中的行，并使用连接进行逻辑操作

Answer 1

在*之前使用表名来只选择特定表的行

SELECT `task`.* 
FROM  `task` 
INNER JOIN  `project` ON project.id = task.projectID 
                     AND project.online = 1

并使用内部连接。参见 this great explanation of joins