Rendre la requête SQL plus efficace

Question

Comment rendre cette requête SQL plus efficace?

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; 

J'ai déjà des index sur les colonnes price et colour, donc je suis à la recherche d'une meilleure façon d'agréger les données.

J'ai examiné en utilisant GROUP BY, HAVING, les auto-jointures et les fonctions de fenêtre, mais je n'arrive pas à obtenir le même résultat.

Toutes les suggestions très appréciées.

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

Selon la façon dont votre base de données gère les expressions booléennes, ceci:

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

ou cette

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; 

pourrait aider.

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 

Cela vous donnera

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

etc.