Question

如何提高此SQL查询的效率？

SELECT 
  (SELECT COUNT(*) FROM table WHERE price < 10) AS priceUnder10,
  (SELECT COUNT(*) FROM table WHERE price BETWEEN 10 AND 20) AS price10to20,
  (SELECT COUNT(*) FROM table WHERE price > 20) AS priceOver20,
  (SELECT COUNT(*) FROM table WHERE colour = 'Red') AS colourRed,
  (SELECT COUNT(*) FROM table WHERE colour = 'Green') AS colourGreen,
  (SELECT COUNT(*) FROM table WHERE colour = 'Blue') AS colourBlue;

我已经在price和colour列上添加了索引，因此我正在寻找一种更好的方法来聚合数据。

我已经研究过使用GROUP BY，HAVING，自联接和窗口函数，但无法弄清楚如何实现相同的结果。

任何建议都非常感谢。

Answer 1

SELECT 
       COUNT(CASE WHEN price < 10 THEN 1 END) AS priceUnder10,
       COUNT(CASE WHEN price BETWEEN 10 AND 20 THEN 1 END) AS price10to20,
       COUNT(CASE WHEN price> 20 THEN 1 END) AS priceOver20,
       COUNT(CASE WHEN colour = 'Red' THEN 1 END) AS colourRed,
       COUNT(CASE WHEN colour = 'Green' THEN 1 END) AS colourGreen,
       COUNT(CASE WHEN colour = 'Blue' THEN 1 END) AS colourBlue
from YourTable  
WHERE price IS NOT NULL OR  colour IN ('Red','Green','Blue' )

Answer 2

根据数据库处理布尔表达式的方式，这个：

select sum(price<10),sum(price between 10 and 20)...  from tab;

或者

select sum(case when price<10 then 1 else 0 end),sum(case when price between 10 and 20 then 1 else 0 end)...  from tab;

可能有帮助。

Answer 3

SELECT count(*) as products, 

if(price < 10, 'price band 1',
 if (price between 10 and 20, 'price band 2',
  'price band 3'
 )
) as priceband,
  t.colour

from table t
group by t.colour, pricebrand

那会给你

products    colour    priceband
53          red       price band 1
65          red       price band 2
12          blue      price band 1
23          blue      price band 2

等

使SQL查询更有效

3 个答案: