本文详细解析了SQL中七种不同的联表查询方法，包括左连接、右连接、内连接、全外连接等，每种方法都通过实例进行了说明，帮助读者深入理解并掌握SQL联表查询技巧。
1、select a.*,b.* from tableA a left join tableB b on a.key = b.key;
2、select a.*,b.* from tableA a right join tableB b on a.key = b.key;
3、select a.*,b.* from tableA a inner join tableB b on a.key = b.key;
4、select a.*,b.* from tableA a left join tableB b on a.key = b.key where b.key is null;
5、select a.*,b.* from tableA a left join tableB b on a.key = b.key where a.key is null;
6、select a.*,b.* from tableA a full outer join tableB b on a.key = b.key;
7、select a.*,b.* from tableA a full outer join tableB b on a.key = b.key where a.key is null or b.key is null;
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