现在有Teacher表
以及Age_J表
我们希望使用Teacher中的Age作为判别对象，将Age_LVL左连接到Teacher表中
select t.t_no,t.t_name,t.t_age ,a.age_lvl from teacher t left join age_j a on t.t_age between a.min_rng and a.max_rng
这里的Age_lvl表是没有值重叠的，如果我们的Age_lvl表变更一下，包含值重叠的情况
再次运行sql语句，得到的结果就有差异了
描述完了。把相关测试建表语句的数据贴一下
create table AGE_J ( age_lvl VARCHAR2(10), min_rng INTEGER, max_rng INTEGER ); create table TEACHER ( t_no NUMBER(5) not null, t_name VARCHAR2(8), t_age NUMBER(3) ); insert into age_j (AGE_LVL, MIN_RNG, MAX_RNG)values (‘青年‘, 18, 29); insert into age_j (AGE_LVL, MIN_RNG, MAX_RNG)values (‘中年‘, 30, 45); insert into age_j (AGE_LVL, MIN_RNG, MAX_RNG)values (‘壮年‘, 46, 59); insert into age_j (AGE_LVL, MIN_RNG, MAX_RNG)values (‘老年‘, 60, 89); insert into TEACHER (T_NO, T_NAME, T_AGE)values (10002, ‘李大钊‘, 24); insert into TEACHER (T_NO, T_NAME, T_AGE)values (10003, ‘毕淑敏‘, 30); insert into TEACHER (T_NO, T_NAME, T_AGE)values (10004, ‘朱自清‘, 59); insert into TEACHER (T_NO, T_NAME, T_AGE)values (10008, ‘闻一多‘, 26); commit;