SQL 连接 JOIN 例解。（左连接，右连接，全连接，内连接，交叉连接，自连接）
很易懂的例子解说http://www.cnblogs.com/eflylab/archive/2007/06/25/794278.html
右连接,等号右侧的所有记录都会显示,无论在左侧是否得到匹配
关于左连接、右连接、外接连总结
在9i以前可以这么写:
左联：
select a.id,a.name,b.address from a,bwhere a.id=b.id(+)
右联:
select a.id,a.name,b.address from a,bwhere a.id(+)=b.id
外联
SELECT a.id,a.name,b.addressFROM a,bWHERE a.id = b.id(+)UNIONSELECT b.id,'' name,b.addressFROM bWHERE NOT EXISTS (SELECT * FROM aWHERE a.id = b.id);
在9i以上，已经开始支持SQL99标准，所以，以上语句可以写成：
默认内部联结：
select a.id,a.name,b.address,c.subjectfrom (a inner join b on a.id=b.id)inner join c on b.name = c.namewhere other_clause
左联
select a.id,a.name,b.addressfrom a left outer join b on a.id=b.idwhere other_clause
右联
select a.id,a.name,b.addressfrom a right outer join b on a.id=b.idwhere other_clause
外联
select a.id,a.name,b.addressfrom a full outer join b on a.id=b.idwhere other_clauseorselect a.id,a.name,b.addressfrom a full outer join b using (id)where other_clause
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