请问下,有两张表:a(uer_id number,class_id number),b(class_id number,class_name varchar2(100));现在要判断a表的class_id是否存在表b的class_id,如果存在则取出a表的class_id和b中相对应得class_name,不存在只列出a表的class_id,class_name为空。
紧急,先谢谢各位的帮忙。
紧急,先谢谢各位的帮忙。
select a.class_id,b.class_name from a left join b where a.uerid=b.uerid
FROM A
LEFT JOIN B
ON A.CLASS_ID = B.CLASS_ID
SELECT A.CLASS_ID, B.CLASS_NAME
FROM A,B
where A.CLASS_ID=B.CLASS_ID(+)
显示所有user及其class:
select a.uer_id, a.class_id, b.class_nam
from a, b
where a.class_id = b.class_id(+)只显示a表中的class_id 及b表中的class_nam
select distinct a.class_id, b.class_nam
from a, b
where a.class_id = b.class_id(+)
FROM A,B
where A.CLASS_ID=B.CLASS_ID(+)