select case trunc(sysdate) 
           when to_date('2022/10/11', 'YYYY/MM/DD')  
           then '#JoelKallmanDay' 
       end as hashtag 
  from dual

declare 
  l_hashtag varchar2(100); 
  l_date    date;   
begin 
    l_date := trunc(sysdate); 
    -- 
    case l_date  
        when to_date('2022/10/11', 'YYYY/MM/DD')  
        then l_hashtag := '#JoelKallmanDay'; 
    end case; 
    -- 
    dbms_output.put_line(l_hashtag); 
end; 

declare 
  l_hashtag varchar2(100); 
  l_date    date;   
begin 
    l_date := trunc(sysdate); 
    -- 
    l_hashtag := case l_date  
                     when to_date('2022/10/11', 'YYYY/MM/DD')  
                     then '#JoelKallmanDay' 
                 end; 
    -- 
    dbms_output.put_line(l_hashtag); 
end; 

create function f_case_expression_test (p_date in date)  
       return varchar2 is 
   l_hashtag varchar2(100); 
begin 
    case p_date  
        when to_date('2022/10/11', 'YYYY/MM/DD')  
        then l_hashtag := '#JoelKallmanDay'; 
    end case; 
    -- 
    return l_hashtag; 
end f_case_expression_test; 

select f_case_expression_test(trunc(sysdate)) from dual