[英]Join columns from tables and merge rows with same id
我正在处理SQL查询,但我完全迷失了联接。 希望您能够为您提供帮助:)
我的问题是来自单独表的行没有合并到具有相同ID的一行中。 很长时间以来,加入使我感到困惑,因此我们将不胜感激。
我有以下表格:
Students
id
StudentCredits
sum_credits
StudentMandatoryCredits
branch_credits
program_credits
我正在尝试创建一个查询,该查询将给我这样的行:
id - sum_credits - branch_credits - program_credits
another_id - sum_credits - branch_credits - program_credits
a_third_id - sum_credits - branch_credits - program_credits
这是我能想到的最好的方法:
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
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
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