mysql 统计一天24小时数据默认补0SQL

select a.click_date,ifnull(b.count,0) as count
from (
   SELECT 0  as click_date
    union all
    SELECT 1 as click_date
    union all
    SELECT 2 as click_date
    union all
    SELECT 3 as click_date
    union all
    SELECT 4 as click_date
    union all
    SELECT 5 as click_date
    union all
    SELECT 6 as click_date
union all
    SELECT 7 as click_date
union all
    SELECT 8 as click_date
union all
    SELECT 9 as click_date
union all
    SELECT 10 as click_date
union all
    SELECT 11 as click_date
union all
    SELECT 12 as click_date
union all
    SELECT 13 as click_date
union all