创建视图 - 声明一个变量答案

【问题标题】：Create View - Declare a variable创建视图 - 声明一个变量
【发布时间】：2017-04-10 02:34:50
【问题描述】：

我正在创建一个使用 STUFF 函数的视图。我想将STUFF 的结果放在一个变量中以供我查看。我遇到的问题是声明我的变量。它给了我消息 “'DECLARE' 附近的语法不正确。期待 '(' 或 SELECT。” 我已经有 '(' 在那里。我尝试在它前面放一个 BEGIN。我已尝试将其放在 SELECT 单词之后。但似乎没有任何效果，我在搜索中找不到解决方案。我使用的是 SQL Server 2012

CREATE VIEW [AQB_OB].[GISREQUESTEDBURNS] 
AS

(DECLARE @CONDITIONS AS varchar(20)
SET @CONDITIONS = (SELECT DISTINCT BD.[RequestedBurnsID]
,[ConditionsReasonsID] = STUFF((SELECT ', ' + CONVERT(VARCHAR (20),[ConditionsReasonsID]) FROM [AQB_OB].[BurnDecisions] WHERE [RequestedBurnsID]= BD.[RequestedBurnsID] ORDER BY [RequestedBurnsID] ASC
FOR XML PATH ('')) , 1 , 1, '') FROM
[AQB_OB].[BurnDecisions] BD)

SELECT RB.[RequestedBurnsID] AS REQUESTEDBURNID
  ,BUY.[BurnYear] AS BURNYEAR
  ,CY.[CurrentYear] AS CURRENTYEAR
  ,RB.[BurnSitesID] AS BURNSITESID
  ,[BurnerID] AS BURNERID
  ,[Contact] AS CONTACT
  ,[BurnDecision] AS BURNDECISION
  ,RB.[Comment] AS COMMENT
  ,@CONDITIONS AS CONDITIONS
FROM [AQB_MON].[AQB_OB].[RequestedBurns] RB
LEFT join AQB_MON.[AQB_OB].[PileDryness] PD on RB.[PileDrynessID] = PD.[PileDrynessID]
inner join AQB_MON.[AQB_OB].[BurnYear] BUY on BUY.BurnYearID = BP.BurnYearID
inner join AQB_MON.[AQB_OB].[CurrentYear] CY on CY.CurrentYearID = BUY.CurrentYearID

GO

【问题讨论】：

您不能在视图中声明变量。用户存储过程或函数。
这能回答你的问题吗？ SQL Views - no variables?

标签： sql-server tsql sql-view declare

【解决方案1】：

您不能在视图中声明变量。你能把它做成一个函数或存储过程吗？

编辑 - 您也可以将某些内容放入 CTE (Common Table Expression) 并将其保留为视图。

例如

WITH conditions as 
(
 ... do the STUFF here
)
SELECT blah
FROM blah
INNER JOIN conditions
(or CROSS JOIN conditions if its just one row, I can't quite decipher what your data is like)

【讨论】：

它让我执行with conditions as ( .. ) 和left join 但是在我看来如何为conditions 创建一个列，因为它不喜欢conditions
"conditions" 将被视为一个表格，因此它将是 conditions.ConditionsReasonsID。
@Ahmed 的回答可能也不错 - 子查询而不是 cte
我能够使用ConditionReasonID。感谢您与我合作。
使用 CTE 的缺点是结果视图无法被索引

【解决方案2】：

这是一个示例查询，它使用 CTE (Common Table Expression) 来很好地模拟内部变量构造，正如 James Casey 所描述的那样。您可以在您的 SQL Server 版本中测试运行它。

CREATE VIEW vwImportant_Users AS
WITH params AS (
    SELECT 
    varType='%Admin%', 
    varMinStatus=1)
SELECT status, name 
    FROM sys.sysusers, params
    WHERE status > varMinStatus OR name LIKE varType

SELECT * FROM vwImportant_Users

产出输出：

status  name
12      dbo
0       db_accessadmin
0       db_securityadmin
0       db_ddladmin

也可以通过JOIN

WITH params AS ( SELECT varType='%Admin%', varMinStatus=1)
SELECT status, name 
    FROM sys.sysusers INNER JOIN params ON 1=1
    WHERE status > varMinStatus OR name LIKE varType

也可以通过CROSS APPLY

WITH params AS ( SELECT varType='%Admin%', varMinStatus=1)
SELECT status, name 
    FROM sys.sysusers CROSS APPLY params
    WHERE status > varMinStatus OR name LIKE varType

【讨论】：

【解决方案3】：

尝试将条件子查询直接放在视图选择语句中。您可以将 XML 转换为 VARCHAR(20)。

CREATE VIEW [AQB_OB].[GISREQUESTEDBURNS] 
AS    
SELECT RB.[RequestedBurnsID] AS REQUESTEDBURNID
  ,BUY.[BurnYear] AS BURNYEAR
  ,CY.[CurrentYear] AS CURRENTYEAR
  ,RB.[BurnSitesID] AS BURNSITESID
  ,[BurnerID] AS BURNERID
  ,[Contact] AS CONTACT
  ,[BurnDecision] AS BURNDECISION
  ,RB.[Comment] AS COMMENT,

 (
     SELECT DISTINCT BD.[RequestedBurnsID],
             [ConditionsReasonsID] = STUFF((SELECT ', ' + CONVERT(VARCHAR (20),     [ConditionsReasonsID]) FROM [AQB_OB].[BurnDecisions] 
     WHERE [RequestedBurnsID]= BD.[RequestedBurnsID] ORDER BY [RequestedBurnsID] ASC
    FOR XML PATH ('')) , 1 , 1, '') FROM
    [AQB_OB].[BurnDecisions] BD
 ) AS CONDITIONS

FROM [AQB_MON].[AQB_OB].[RequestedBurns] RB
LEFT join AQB_MON.[AQB_OB].[PileDryness] PD on RB.[PileDrynessID] = PD.[PileDrynessID]
inner join AQB_MON.[AQB_OB].[BurnYear] BUY on BUY.BurnYearID = BP.BurnYearID
inner join AQB_MON.[AQB_OB].[CurrentYear] CY on CY.CurrentYearID = BUY.CurrentYearID

【讨论】：

当我这样做时，我收到了错误Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.。我认为这是由于STUFF 功能。

【解决方案4】：

或者使用 CTE（公用表表达式）作为子选择，例如：

WITH CTE_Time(Clock)
AS(
    SELECT 11 AS [Clock] -- set var
)

SELECT 
    DATEPART(HOUR, GETDATE()) AS 'actual hour',
    CASE
        WHEN DATEPART(HOUR, GETDATE()) >= (SELECT [Clock] FROM CTE_Time) THEN 'after'
        ELSE 'before'
    END AS [Data]

【讨论】：