如果然後其他人

Question

工作在一個視圖，從兩個表中拉，但是在一個表中，我需要選擇一個領域或另一個取決於第三..這是如果別人有我殘缺。

Create view as 
     select 
      pens.PartNo, 
      pens.Title, 
      ranges.weight 
      if(pens.SpeacialOffer = 1 then pens.offer as Price else pens.Price) 
     from 
      pens, ranges 
     where 
      pens.penrange = ranges.id; 

如果特別優惠活動失敗，則該視圖需要提供報價，否則需要拉動報價。

Answer 1

你需要的是一個CASE operator：

CASE 
    WHEN condition 
    THEN value_a 
    ELSE value_b 
END 

所以你的情況：

CASE 
    WHEN pens.SpeacialOffer = 1 
    THEN pens.offer 
    ELSE pens.price 
END 

這將替換您的SELECT狀態中的整個列定義換貨，所以整個角度的：

Create View as 
    Select 
     pens.PartNo, 
     pens.Title, 
     ranges.weight, 
     Case 
      When pens.SpeacialOffer = 1 
      Then pens.offer 
      Else pens.price 
     End as Price 
    From 
     pens, ranges 
    Where 
     pens.penrange = ranges.id; 

Answer 2

的使用情況，也轉換查詢，以顯式連接的隱含而不是加入

select pens.PartNo, 
     pens.Title, 
     ranges.weight,  
     (Case when 
     pens.SpeacialOffer = 1 then 
     pens.offer else pens.Price 
     end) as Price 
     FROM pens, 
     JOIn ranges 
     ON pens.penrange = ranges.id; 

Answer 3

這裏有一種方法：

Create view as select 
    pens.PartNo, 
    pens.Title, 
    ranges.weight, 
    (pens.SpeacialOffer * pens.offer + (1 - pens.SpeacialOffer) * pens.price) as Price 
from 
    pens, 
    ranges 
where 
    pens.penrange = ranges.id;