postgres レコード年項目の値が存在したら、CASE文にて経過年数を表示

select
    m_i_age_year,
    CASE WHEN m_i_age_year = ''  THEN 0
         WHEN m_i_age_year <> '' THEN to_number(TO_CHAR(current_timestamp, 'yyyy'), '0000000000')-to_number(m_i_age_year, '0000000000')
    END  AS m_i_age_year_course_label
from tbl_estate_article;