[英]left join doesn't work - its ignoring the records of the left table
我有3张桌子
表客户
ID NUMBER NAME
--------------------------------------
1 12345 Apple
2 23456 Orange
3 25896 Banana
表帐户
ID CUST_NUMBR TYPE BILLING_FK
-------------------------------------
1 12345 B 9876
2 23456 R 8765
3 25896 R 7654
表计费
ID Start_Date End_Date
-------------------------------------
1 BLAH BLAH
2 BLAH BLAH
3 BLAH BLAH
关系
CUSTOMER.NUMBER = ACCOUNT.CUST_NUMBR
ACCOUNT.BILLING_FK = BILLING.ID
有时,找不到客户的帐户,在这种情况下,开始日期必须为空。
如果我尝试左加入,如果没有帐户,则看不到客户。
select name,number,start_date
from customer left join account on customer.number = account.cust_number,
billing
where account.billing_fk = billing.id
如果没有该客户的帐户,如何将开始日期设为空。
您的条件为account.billing_fk = billing.id
将您的LEFT JOIN
变成INNER JOIN
。 几乎消除了所有NULL
条目。
select name,number,start_date
from customer
left join account on customer.number = account.cust_number
left join billing on account.billing_fk = billing.id
由于您的where子句中有以下语句,因此无法使用:
account.billing_fk = billing.id
尝试将其移到left join section
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