sql - 在sql server的一个视图中组合多个UNION

Question

我想创建一个如下视图。

Create view SomeView
AS
SELECT DISTINCT ISNULL(ID,'ID') as Id, 
ISNULL(ID,'unknown') + ':' + 'ID' AS label,
ISNULL(ID,'unknown') AS [value]
FROM [test].[emp].[OrgView]
  UNION
SELECT DISTINCT ISNULL(EMP_ID,'ID') as Id, 
ISNULL(EMP_ID,'unknown') + ':' + 'EMP_ID' AS label,
ISNULL(EMP_ID,'unknown') AS [value]
FROM [test].[emp].[OrgView]
  UNION
SELECT DISTINCT ISNULL(LICENSE_NO,'LICENSE_NO') as Id, 
ISNULL(LICENSE_NO,'unknown') + ':' + 'LICENSE_NO' AS label,
ISNULL(LICENSE_NO,'unknown') AS [value]
FROM [test].[emp].[OrgView]
.
.
.
.
.
10 such selects

那么在这种情况下，是否会为每个选择块进行调用，还是只会调用一次？我不希望这对每个 select 进行 10 次不同的调用。如果您知道，请向我指出一些在线资源。

标签： sqlsql-serversql-tuning

Answer 1

使用APPLY：

SELECT DISTINCT COALESCE(v.ID, v.id_default) as Id, 
       COALESCE(o.FIRST_NAME, 'unknown') + ':' + v.name_suffix AS label,
       COALESCE(o.VALUE, 'unknown') AS [value]
FROM [test].[emp].[OrgView] o CROSS APPLY
     (VALUES (o.ID, 'ID', 'Unknown'),
             (o.EMP_ID, 'ID', 'EMP'),
             (o.LICENSE, 'LICENSE_NO', 'LICENSE_NO'), . . . 
     ) v(ID, id_default, name_suffix);