Question

由于业务规则最近发生了变化，一组数据过去常常存储在一个数据库中，现在存储在同一服务器上的不同数据库中。当前设置的东西，如果用户想要查询与业务规则更改时间重叠的日期范围内的数据，他们将被迫在其代码中使用IF语句。

我想创建一个表值函数，它将为进行此类查询的用户抽象业务规则中的此更改。目前我正在尝试执行与此类似的代码：

CREATE FUNCTION dbo.someFunction (date DATETIME)
RETURNS TABLE
AS
RETURN
IF (date <= business_rules_change_date)
BEGIN
SELECT (A select statement)
FROM (Old Database)
WHERE (criteria)
END
ELSE
SELECT (A similar select statement)
FROM (New Database)
JOIN (A Join Statement)
WHERE (criteria)
GO

我被告知IF语句周围存在语法错误。我的问题有一个很好的解决方案吗？

Answer 1

您可以尝试这样的事情

CREATE FUNCTION dbo.someFunction (date DATETIME)
  RETURNS @RtnTable TABLE (SomeValue varchar(250))
AS
BEGIN
  IF (date <= business_rules_change_date)
  BEGIN
     INSERT INTO @RtnTable
     SELECT (A select statement)
     FROM (Old Database)
     WHERE (criteria)
  END
  ELSE
  BEGIN 
     INSERT INTO @RtnTable
     SELECT (A similar select statement)
     FROM (New Database)
     JOIN (A Join Statement)
     WHERE (criteria)
  END

  RETURN
END

此示例假定您的函数返回带有单个varchar列的结果集。根据您的IF条件，您可以使用不同的SELECT语句的结果填充它。根据需要进行调整。

Answer 2

或者正如Yuriy建议你可以使用像这样的多语句表值函数...

CREATE FUNCTION dbo.someFunction (date DATETIME)
RETURNS @TABLE TABLE 
(
     -- Define the structure of table here
)
AS
BEGIN
  IF (date <= business_rules_change_date)
   BEGIN
    INSERT INTO @TABLE
    SELECT (A select statement)
    FROM (Old Database)
    WHERE (criteria)
   END  
ELSE
  BEGIN 
    INSERT INTO @TABLE
    SELECT (A similar select statement)
    FROM (New Database)
    JOIN (A Join Statement)
    WHERE (criteria)
  END

  RETURN    
END

Answer 3

内联表值函数不能包含IF语句。您可以这样重新组织查询：

CREATE FUNCTION dbo.someFunction (date DATETIME)
RETURNS TABLE
AS
RETURN
    SELECT (A select statement)
    FROM (Old Database)
    WHERE (criteria) AND (date <= business_rules_change_date)
    UNION
    SELECT (A similar select statement)
    FROM (New Database)
    JOIN (A Join Statement)
    WHERE (criteria) AND (date > business_rules_change_date)
GO

if语句确定在Table-Value Function中返回哪个SELECT

3 个答案: