以下查询只返回客户没有致电客户服务中心的行。在此查询中，数据库服务器
对 customer 和 cust_calls 表的 customer_num 列执行外连接之后在 WHERE 子句中应用过
滤器。
图: 查询
SELECT c.customer_num, c.lname, c.company, c.phone,?
?u.call_dtime, u.call_descr?
?FROM customer c LEFT OUTER JOIN cust_calls u?
?ON c.customer_num = u.customer_num?
?WHERE u.customer_num IS NULL;
除了前面的示例之外，下列示例显示了可与 ANSI 连接语法配合使用的各种查询构造类
型：
SELECT *
?FROM (t1 LEFT OUTER JOIN (t2 LEFT OUTER JOIN t3 ON t2.c1=t3.c1)
?ON t1.c1=t3.c1) JOIN (t4 LEFT OUTER JOIN t5 ON t4.c1=t5.c1)
?ON t1.c1=t4.c1;
?
?SELECT *
?FROM (t1 LEFT OUTER JOIN (t2 LEFT OUTER JOIN t3 ON t2.c1=t3.c1)?
?ON t1.c1=t3.c1),?
?(t4 LEFT OUTER JOIN t5 ON t4.c1=t5.c1)
?WHERE t1.c1 = t4.c1;
?
?SELECT *
?FROM (t1 LEFT OUTER JOIN (t2 LEFT OUTER JOIN t3 ON t2.c1=t3.c1)
?ON t1.c1=t3.c1) LEFT OUTER JOIN (t4 JOIN t5 ON t4.c1=t5.c1)
?ON t1.c1=t4.c1;
?
?SELECT *
?FROM t1 LEFT OUTER JOIN (t2 LEFT OUTER JOIN t3 ON t2.c1=t3.c1)
?ON t1.c1=t2.c1;
?
?SELECT *
?FROM t1 LEFT OUTER JOIN (t2 LEFT OUTER JOIN t3 ON t2.c1=t3.c1)
?ON t1.c1=t3.c1;
?
?SELECT *
?FROM (t1 LEFT OUTER JOIN t2 ON t1.c1=t2.c1)
?LEFT OUTER JOIN t3 ON t2.c1=t3.c1;
?
?SELECT *
?FROM (t1 LEFT OUTER JOIN t2 ON t1.c1=t2.c1)
?LEFT OUTER JOIN t3 ON t1.c1=t3.c1;
?
?SELECT *
?FROM t9, (t1 LEFT JOIN t2 ON t1.c1=t2.c1),
?(t3 LEFT JOIN t4 ON t3.c1=10), t10, t11,
?(t12 LEFT JOIN t14 ON t12.c1=100);
?
?SELECT * FROM
?((SELECT c1,c2 FROM t3) AS vt3(v31,v32)
?LEFT OUTER JOIN
?( (SELECT c1,c2 FROM t1) AS vt1(vc1,vc2)
?LEFT OUTER JOIN
?(SELECT c1,c2 FROM t2) AS vt2(vc3,vc4)
?ON vt1.vc1 = vt2.vc3)
?ON vt3.v31 = vt2.vc3);
上面最后一个示例说明了关于派生表的连接。它指定将外查询的 FROM 子句中子查询的
结果和另一个其它两个子查询结果的左外连接的结果进行左外连接。请参阅FROM 子句中
的子查询获得较为简单的符合 ANSI 语法的子查询示例。
