如何根據記錄存在從2個表中選擇1條記錄？

Question

我有2個表，通過查詢說明：

CT_Validation

select ValidationID, Message from CT_Validation 

ValidationID Message 
====================================================== 
IP_Validator Not a valid IP address 
NumbersOnly  Invalid number. 
SSN    Not a valid social security number. 
10Digits  A 10-digit number is required. 

CT_Validation_Lang

select ValidationID, LangID, Message from CT_Validation_Lang 

ValidationID LangID Message 
====================================================== 
SSN   es  Peligro es mi segundo nombre! 

我如何將建立一個連接，這樣，如果LangID = 'es'我會回來：

ValidationID Message 
====================================================== 
IP_Validator Not a valid IP address 
NumbersOnly  Invalid number. 
SSN    Peligro es mi segundo nombre! 
10Digits  A 10-digit number is required. 

...但如果LangID爲空，空，或者不是「ES」，結果將回復到所有英語以外的其他：

ValidationID Message 
====================================================== 
IP_Validator Not a valid IP address 
NumbersOnly  Invalid number. 
SSN    Not a valid social security number. 
10Digits  A 10-digit number is required. 

重要提示：鍵字段是ValidationID和重要的關鍵值在這個例子中是SSN，因爲它存在於兩個表中。

在此先感謝您的任何建議。

Answer 1

我想你想left join和​​3210

select cv.ValidationID, coalesce(cvl.Message, cv.Message) 
from CT_Validation cv 
left join CT_Validation_Lang cvl on cv.ValidationID = cvl.ValidationID 
    and cvl.LangID = 'es' 

這將從CT_Validation_Lang選擇Message，如果它存在LangIDes。連同left join

select 
    ctv.ValidationID, 
    coalesce(
      (select 
      ctvl.Message 
      from 
      CT_Validation_Lang ctvl 
      where 
      ctvl.ValidationID = ctv.ValidationID and 
      LangID = 'es' 
      ), 
      ctv.Message, ' ') as Message 
    from 
    CT_Validation ctv; 

Answer 2

你可以這樣做：

select v.ValidationID, coalesce(vl.message, v.message) as message 
from CT_Validation v left join 
    CT_Validation_Lang vl 
    ON vl.ValidationID = v.ValidationID and vl.LangID = 'es'; 

這將從CT_Validation_Lang選擇消息時，西班牙語翻譯可用。否則，它會選擇原始消息。

Answer 3

喜歡的東西回落到Message。

select a.ValidationID, ISNULL(b.message, a.message) 
from CT_Validation a 
left join CT_Validation_Lang b on a.ValidationID = b.ValidationID and b.LangID = 'es' 

Answer 4

一種方式與CASE

SELECT 
    ctv.ValidationID, 
    CASE WHEN ctvl.LangID = 'es' THEN ctvl.message ELSE ctv.message END AS Message 
FROM CT_Validation ctv 
LEFT JOIN CT_Validation_Lang ctvl ON ctv.ValidationId = ctvl.ValidationId 
    AND ctvl.LangID = 'es' 

Answer 5

使用ISNULL()功能 - ：否則，它會從CT_Validation