SQL DB2計算模式

Question

我使用DB2和有兩個表：

用戶：

• ID - 關鍵
• 教育（整數值表示級）
• 年齡

付款方式：

• 店
• 總和
• ID - 外鍵

我要計算教育的統計模式，每家商店，現在我想類似的東西： 1）計算店X模式：

select u.education    
    from users u, payments p 
    where u.id = p.id AND    
    p.shop = 'X'  
    group by u.education order by count(*) desc 
    fetch first 1 rows only;      

此查詢工作正常

2）計算教育的模式，每店：

select p.Shop as Shop,      
    avg(u.age) as AvgAge,          
    (select u1.education           
     from users u1          
     where u1.id = p.id         
     group by u1.education           
     order by count(*) desc           
     fetch first 1 rows only) as ModeEdu        
    from users u, payments p      
    where u.id = p.id          
    group by p.Shop;       

這個查詢給出了一個錯誤：

SQLCODE = -119，ERROR：確定了具有 子句中的列或表達式無效

Answer 1

在這裏你去。我已經更改爲「現代」連接語法。你20年前使用的語法是「老」。我強烈推薦使用新的語法。

WITH eduCount AS 
(
    select u1.id, u1.education, count(*) as c 
    from users u1 
    group by u1.id u1.education           
), byUser AS 
( 
    select id, education, c, 
    ROW_NUMBER() OVER (PARTITION BY id, education ORDER BY c DESC) AS RN 
    from eduCount 
) 
select p.Shop as Shop,      
    avg(u.age) as AvgAge,          
    max(byUser.education) as ModeEdu 
from users u 
join payments p on u.id = p.id 
left join byUser on byUser.id = u1.id AND rn = 1 
group by p.Shop;