連接表中的列並合並具有相同ID的行

Question

我正在處理SQL查詢，但我完全迷失了聯接。 希望您能夠為您提供幫助：)

我的問題是來自單獨表的行沒有合並到具有相同ID的一行中。 很長時間以來，加入使我感到困惑，因此我們將不勝感激。

我有以下表格：

Students
id

StudentCredits
sum_credits

StudentMandatoryCredits
branch_credits
program_credits

我正在嘗試創建一個查詢，該查詢將給我這樣的行：

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

這是我能想到的最好的方法：

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