基于另一列中的值替换列的值的SQL查询

我在SQL Server中有一个表，它的数据如下：

Costing_ID CostingName CostingNumber CostingNumberSuffix StartDate
1          Test        1234                              2014-04-01
2          Test 2      1234          AA                  2014-04-06
3          Test 3      5668                              2014-04-09
4          Test 4      1234          AB                  2014-04-14

我需要生成一个返回所有行的视图，但将CostingNumberSuffix不为空的项目的StartDate替换为相应CostingNumber的StartDate，该StartDate为空

WITH CTE AS
(
    SELECT CostingNumber, StartDate
    FROM <tablename>
    WHERE CostingNumberSuffix IS NULL
)
SELECT
    T.Costing_ID,
    T.CostingName,
    T.CostingNumber,
    T.CostingNumberSuffix,
    ISNULL(CTE.StartDate, T.StartDate) AS StartDate
FROM <tablename> T
LEFT OUTER JOIN CTE
ON T.CostingNumber = CTE.CostingNumber

因此，我的查询应返回以下内容：

   Costing_ID CostingName CostingNumber CostingNumberSuffix StartDate
    1          Test        1234                              2014-04-01
    2          Test 2      1234          AA                  2014-04-01
    3          Test 3      5668                              2014-04-09
    4          Test 4      1234          AB                  2014-04-01

---

我该怎么做呢

请尝试此查询。我还没有测试过，但你知道了：

SELECT
    Costing_ID,
    CostingName,
    CostingNumber,
    CostingNumberSuffix,
    CASE
        WHEN CostingNumberSuffix != ''
            THEN (SELECT s.StartDate FROM table s WHERE s.CostingNumber = t.CostNumber and s.CostNumberSuffix = '')
        ELSE
            StartDate
    END 
FROM table t

---

以下是一个SQL查询，用于根据列中的值替换另一列中的值：

select t1.Costing_ID, t1.CostingName, t1.CostingNumber,
  t1.CostingNumberSuffix,
  coalesce (t2.StartDate, t1.StartDate)
from <table name> t1
left join (select * from <table name> where CostingNumberSuffix = '') t2
on t1.costingnumber = t2.costingnumber

SQL Server 2012：

select Costing_ID, CostingName, CostingNumber, CostingNumberSuffix,
first_value(StartDate) over (partition by CostingNumber order by CostingNumberSuffix
    rows unbounded preceding) as StartDate
from Costing
order by Costing_ID

---

此解决方案使用公共表表达式a.k.a CTE。CTE查找CostingNumberSuffix为空的项目的起始日期

WITH CTE AS
(
    SELECT CostingNumber, StartDate
    FROM <tablename>
    WHERE CostingNumberSuffix IS NULL
)
SELECT
    T.Costing_ID,
    T.CostingName,
    T.CostingNumber,
    T.CostingNumberSuffix,
    ISNULL(CTE.StartDate, T.StartDate) AS StartDate
FROM <tablename> T
LEFT OUTER JOIN CTE
ON T.CostingNumber = CTE.CostingNumber

---

测试3的日期是什么？测试3有自己的成本编号，没有后缀，所以它会保留起始日期。如果我有一个成本编号为5668、后缀为ZZ的测试6，它将获得测试3的起始日期等。每个成本编号上只有一个没有后缀的记录。