更有效的方式來運行日期/ yyyy查詢？

Question

我使用以下查詢相當多，但我很確定必須有一個更有效的方法來做到這一點。

基本上，我指望的人出生在幾十年中，從用戶表內：

select count(*) as howmany, yyyy from bday where (((yyyy > '1949') 
AND (yyyy < '1961')) AND (user_id = '63')) UNION 
select count(*) as howmany, yyyy from bday where (((yyyy > '1959') 
AND (yyyy < '1971')) AND (user_id = '63')) UNION 
select count(*) as howmany, yyyy from bday where (((yyyy > '1969') 
AND (yyyy < '1981')) AND (user_id = '63')) UNION 
select count(*) as howmany, yyyy from bday where (((yyyy > '1979') 
AND (yyyy < '1991')) AND (user_id = '63')) UNION 
select count(*) as howmany, yyyy from bday where (((yyyy > '1989') 
AND (yyyy < '2001')) AND (user_id = '63')) 

Answer 1

就可以計算出十年並用它來組的用戶：

SELECT 
    COUNT(id) AS howmany, 
    CEIL((`yyyy`+1)/10) AS decade, 
    yyyy 
FROM `bday` 
GROUP BY decade 

Answer 2

到算出幾十年出生的人：

select substring(yyyy, 1, 3) || '0''s' decade, count(*) howmany 
from bday 
group by decade