從表中合併列，併合並具有相同ID的行

Question

我正在處理SQL查詢，並且我完全迷失了自己的聯接。希望你能夠協助:)

我的問題是，從單獨的錶行不合併到一個單一的行中，他們都有相同的ID。長久以來，我一直對我一直感到困惑，因此任何幫助都將不勝感激。

我有以下表格：

Students 
id 

StudentCredits 
sum_credits 

StudentMandatoryCredits 
branch_credits 
program_credits 

我試圖創建一個查詢，這將使我行這樣的：

id   - sum_credits - branch_credits - program_credits 
another_id - sum_credits - branch_credits - program_credits 
a_third_id - sum_credits - branch_credits - program_credits 

這是最好的，我可以拿出雖然：

id - sum_credits - branch_credits -  [empty] 
id - sum_credits -  [empty] - program_credits 

這是我的SQL語句：

SELECT S.id, SC.sum_credits, SMC.branch_credits, SMC.program_credits 
FROM Students S 
LEFT JOIN StudentCredits SC ON S.id = SC.id 
LEFT JOIN StudentMandatoryCredits SMC ON S.id = SMC.id 
ORDER BY id 

Answer 1

嘗試使用：

SELECT S.id, SUM(SC.sum_credits), SUM(SMC.branch_credits), SUM(SMC.program_credits) 
FROM Students S 
LEFT JOIN StudentCredits SC ON S.id = SC.id 
LEFT JOIN StudentMandatoryCredits SMC ON S.id = SMC.id 
GROUP BY S.id 
ORDER BY S.id