mysql - 在 MySQL 中操作字段的最有效方法是什么？

Question

我有以下查询:

SELECT DATE(utimestamp) as utimestamp, name, data*2000000 from tData 
where utimestamp BETWEEN '2016-01-01 00:00:00' AND '2016-04-16 00:00:00' 
AND name = 'Valor2' and data>20
group by YEAR(utimestamp), MONTH(utimestamp), name 
union
SELECT DATE(utimestamp) as utimestamp, name, data*0.1 from tData 
where utimestamp BETWEEN '2016-01-01 00:00:00' AND '2016-04-16 00:00:00' 
AND name = 'Valor1' and data>20 
group by YEAR(utimestamp), MONTH(utimestamp), name 
order by utimestamp asc

是否有更有效的“数据”操作方式？有没有不使用 UNION 就可以做到这一点的方法？

Answer 1

你可以尝试使用case when then:

SELECT DATE(utimestamp) as utimestamp, name, 
case when name = 'Valor1' then data*0.1
     when name = 'Valor2' then data*2000000 
end
from tData 
where utimestamp BETWEEN '2016-01-01 00:00:00' AND '2016-04-16 00:00:00' 
and data>20 
group by YEAR(utimestamp), MONTH(utimestamp), name 
order by utimestamp asc