菜鸟问题：求教两条SQL语句的含义（每条50分）（急！在线等答案）(100分)

1、SELECT hisData.*<br>FROM client LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; well ON well.clientId = client.id LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; project ON project.wellId = well.id LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; hisData ON hisData.projectId = hisData.projectId<br>WHERE (client.id = '11943988860459749')<br>2、select region.name,client.name,well.no,well.address as wellAddress,project.id as projectId<br>from region left join client on client.townId = region.id <br>&nbsp; &nbsp; &nbsp;left join well on well.clientId = client.id <br>&nbsp; &nbsp; &nbsp;left join project on project.wellId = well.id<br>说明：<br>1、hisData：历史数据记录表；client：取水用户表；well：水井信息记录表；well.clientId：指向取水用户的外键；client.id：取水用户ID号；project：工程信息表；project.wellId：工程信息表.水井ID号；well.id：水井ID号；hisData.projectId：<br>取水工程ID号。<br>2、region.name：行政区划表.行政区名称；client.name：取水用户表.取水户名称；well.no：水井编号；well.address：水井位置；client.townId：取水用户表.所在区县行政区Id号。<br>3、以上两条SQL语句都是对同一数据库进行操作。<br>我越看越糊涂，麻烦各位兄弟姐妹帮忙解释。先谢了！

就是查询语句。。有什么问题吗？？？

SELECT hisData.*//要显示字段的内容<br>FROM client LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; well ON well.clientId = client.id LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; project ON project.wellId = well.id LEFT OUTER JOIN<br>&nbsp; &nbsp; &nbsp; hisData ON hisData.projectId = hisData.projectId//因为相关的信息存放在不同的表中,要通过关联来取数<br>WHERE (client.id = '11943988860459749')//条件过滤.

left outer join: 左外连接。a left outer join b on a.A=b.B，结果是，取a表里面的所有记录。其中，可能只有某些跟b表关联。<br>而如果换作 select a.*, b.* from a, b where a.A=b.B的话，那就只有符合a.A=b.B这个条件的记录才会被选择出来。<br>一个是选择a表的全部记录，一个只是选择符合条件的某些记录。这就是区别。

谢谢各位哥们！