连接具有相同键但不同字段的两个表

Question

我有两个 table 都具有相同的字段除了一个。我想将这两个 table 与生成的 table 结合起来，其中包含来自两者的所有字段，包括每个 table 中不相同的两个字段。即：

假设我有 table order_debit 架构

order_id, date_of_order, debit_balance

5, 2019, 100
2, 2021, 30

和 table order_credit 架构

order_id, date_of_order, credit_balance

1,2020, 35
2,2021, 40

我想要的是最终的 table 架构

order_id, date_of_order, credit_balance, debit_balance

5, 2019, 100, 0
2, 2021, 30, 40
1, 2020, 0, 35

我不知道如何在不获取重复值的情况下进行连接，我认为 order_ids 不会有太多重叠，但肯定会有一些。

Answer 1

您需要将 full join 与 coalesce

一起使用

select
  coalesce(t1.order_id, t2.order_id) as order_id,
  coalesce(t1.date_of_order, t2.date_of_order) as date_of_order,
  coalesce(t1.debit_balance, 0) as debit_balance,
  coalesce(t2.credit_balance, 0) as credit_balance
from t1 
  full join t2
    on t1.order_id=t2.order_id

Answer 2

基本上你想要一个 full join，MySQL 不支持。一个方便的方法是：

select od.order_id, od.date_of_order, od.debit_balance,
       coalesce(oc.credit_balance, 0) as credit_balance
from order_debit od left join
     order_credit oc
     using (order_id, date_of_order)
union all
select oc.order_id, oc.date_of_order, 0, oc.credit_balance
from order_credit oc
where not exists (select 1
                  from order_debit od
                  where od.order_id = oc.order_id and od.date_of_order = oc.date_of_order
                 );

Answer 3

对于MySQL，您可以使用UNION ALL和GROUP BY

SELECT
    order_id, date_of_order, SUM(credit_balance), SUM(debit_balance)
FROM 
(
    SELECT order_id, date_of_order, 0 AS credit_balance, debit_balance FROM tbl_debit
    UNION ALL
    SELECT order_id, date_of_order, credit_balance, 0 AS debit_balance FROM tbl_credit
) FROM t
GROUP BY order_id, date_of_order

连接具有相同键但不同字段的两个表

Joining two tables with same keys but different fields

mysql

sql

relational-database

apache-spark-sql