如何在SQL Server中为一项添加两条记录？

我有一张这样的桌子：

Parent  date        currency_type   currency 
---------------------------------------------
4106    2016/06/11  EUR             3000.00 
2055    2017/06/10  USD             4000000.00  
2055    2017/06/10  EUR             4030000.00  

如果一种美元或欧元类型为空，我有两种类型usd和eur，如何自动添加一行代码

4106    2016/06/11  USD             0

---

谢谢

一个选项是使用包含所有父项、日期和货币类型的日历表进行插入：

INSERT INTO yourTable (Parent, date, currency_type, currency)
SELECT p.Parent, d.date, c.currency_type, 0
FROM (SELECT DISTINCT Parent FROM yourTable) AS p
CROSS JOIN (SELECT DISTINCT date FROM yourTable) AS d
CROSS JOIN (SELECT DISTINCT currency_type FROM yourTable) AS c
LEFT JOIN yourTable t
    ON t.Parent = p.Parent AND
       t.date = d.date AND
       t.currency_type = c.currency_type
WHERE
    t.Parent IS NULL;

---

这一系列交叉联接生成父类型、日期和货币类型的所有可能组合。然后，左侧的反联接将清除当前表中缺少的组合。这种方法假设每个可能的父项、日期和货币类型在当前表中至少存在一次。例如，如果您希望填充当前表中完全缺失的日期，则该操作将失败。在这种情况下，我们必须从头开始完全生成新数据。

您需要UNION ALL，如果这些行不存在，第二个查询将创建这些行：

select * from tablename
union all
select 
  t.parent, 
  t.date,
  case t.currency_type
    when 'EUR' THEN 'USD'
    when 'USD' THEN 'EUR'
  end,
  0
from tablename t
where not exists (
  select 1 from tablename
  where parent = t.parent and currency_type <> t.currency_type
) 
order by parent desc, currency_type

---

使用交叉应用和分组方式

create table #t(
Parent  int,
[date]  date,
currency_type varchar(3),
currency decimal(20,2)
);
insert #t (Parent,[date], currency_type, currency)
values
(4106,'2016/06/11','EUR',3000.00    ),
(2055,'2017/06/10','USD',4000000.00 ),
(2055,'2017/06/10','EUR',4030000.00 )
;


select 
   Parent,[date], c.curr currency_type, max(case currency_type when c.curr then currency else 0 end) currency
from #t t
cross apply(
    select curr
    -- add currencies to the list as needed
    from (values ('EUR'),('USD')) c(curr)
) c
group by Parent,[date], c.curr;

---

感谢这段代码，因为我是sql server中的noob。请注意，此解决方案只处理两种（硬编码的）货币类型。这是要求：我有两种类型usd和EUR感谢这段代码有效，但我是sql server中的noob及其pro级别的noob

create table #t(
Parent  int,
[date]  date,
currency_type varchar(3),
currency decimal(20,2)
);
insert #t (Parent,[date], currency_type, currency)
values
(4106,'2016/06/11','EUR',3000.00    ),
(2055,'2017/06/10','USD',4000000.00 ),
(2055,'2017/06/10','EUR',4030000.00 )
;


select 
   Parent,[date], c.curr currency_type, max(case currency_type when c.curr then currency else 0 end) currency
from #t t
cross apply(
    select curr
    -- add currencies to the list as needed
    from (values ('EUR'),('USD')) c(curr)
) c
group by Parent,[date], c.curr;