PostgreSQL中的条件语句

Question

'select'语句产生一些数据输出序列，如'SL''CL''PL'等，如下图所示

如果数据输出为SL，则应将其转换并显示为“Z”，如果其“CL”为“Q”，如果其“PL”则为“R”

有没有办法实现这个

Answer 1

您可以使用CASE WHEN

select case when dbreed1 = 'SL' then 'Z'
            when dbreed1 = 'CL' then 'Q'
            when dbreed1 = 'PL' then 'R'
            else 'other'
       end dbreed1_mapped

您也可以编写自己的函数：

create or replace function map_breed(_input text) returns text as
$$
    select case when _input = 'SL' then 'Z'
                when _input = 'CL' then 'Q'
           end
$$
language sql;

并称之为：

select map_breed('SL');

Answer 2

create or replace function map_breed(dbreed text) returns text as 
$$ 
   begin 
   select case when dbreed = 'SL' then 'Z' 
               when dbreed = 'CL' then 'Q' end into dbreed; 
   return dbreed;
   end; 
$$ language plpgsql; 

/*and call the function as*/
select map_breed('SL') as breed