从表中合并列，并合并具有相同ID的行

Question

我正在处理SQL查询，并且我完全迷失了自己的联接。希望你能够协助:)

我的问题是，从单独的表行不合并到一个单一的行中，他们都有相同的ID。长久以来，我一直对我一直感到困惑，因此任何帮助都将不胜感激。

我有以下表格：

Students 
id 

StudentCredits 
sum_credits 

StudentMandatoryCredits 
branch_credits 
program_credits 

我试图创建一个查询，这将使我行这样的：

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

这是最好的，我可以拿出虽然：

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

这是我的SQL语句：

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

尝试使用：

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