PostgreSQL--一个查询问题？

Question

现有两张表： 
ls_rss_info 
rss_id   rss_code   user_id   type 
    1             010             1000       0 
    2             020             1000       0 
    3             027             1000       0 
    4             028             1002       0   ls_rss_param 
param_id   param_code   param_name       type 
    1                   010               北京                       0 
    2                   020               广州                       0 
    3                   021               上海                       0 
    4                   027               武汉                       0 
    5                   028               成都                       0 
    6                   029               西安                       0 如何得到如下结果： 
条件：user_id=1000   and   type=0 
param_id   param_code   param_name       bool 
    1                   010               北京                       t 
    2                   020               广州                       t 
    3                   021               上海                       f 
    4                   027               武汉                       t 
    5                   028               成都                       f 
    6                   029               西安                       f 

Answer 1

select a.param_id,
       a.param_code,
       a.param_name,
       case when b.rss_code is null then 't' else 'f' end as bool
from ls_rss_param a left join b
on a.param_code = b.rss_code
where b.user_id = 1000 and b.type =0;