sql - 右表的左连接与 where 子句(必须从右返回 NULL) - Oracle

Question

我有 2 个表 ID 和 Comm。表格如下

 ID                          AppID   Name1       James2       John..100     JeffCommAppID  Comment1      abc1      def1      pqr2      abc2      def2      pqr3      def

I want all appID from ID (First table) and from Comm(Second table) I want only those comment which are equal to abc, rest others should be NULL.

I am using following query, not sure how do I filter comment abc and Null

select id.appid,comm.comment
from id left join comm on
id.appid=comm.appid
where comm.comment = 'abc'

我知道我的逻辑错了，我想弄清楚我应该在哪里改变。任何帮助表示赞赏。

Answer 1

select id.appid,comm.comment
from id 
left join comm 
    on id.appid=comm.appid
    and comm.comment = 'abc'