您应该能够在没有任何IF或CASE的情况下做到这一点

 WHERE 
   (IsNumeric(@OrderNumber) AND
      (CAST OrderNumber AS VARCHAR) = (CAST @OrderNumber AS VARCHAR)
 OR
   (NOT IsNumeric(@OrderNumber) AND
       OrderNumber LIKE ('%' + @OrderNumber))

根据SQL的风格，您可能需要将订单号上的类型转换调整为INT或VARCHAR，这取决于是否支持隐式类型转换。

这是WHERE子句中非常常见的技术。如果你想在WHERE子句中应用一些“If”逻辑，你所需要做的就是在需要应用它的部分中添加一个布尔AND的额外条件。

你根本不需要IF语句。

WHERE
    (IsNumeric(@OrderNumber) = 1 AND OrderNumber = @OrderNumber)
OR (IsNumeric(@OrderNumber) = 0 AND OrderNumber LIKE '%' + @OrderNumber + '%')

下面的示例将查询作为布尔表达式的一部分执行，然后根据布尔表达式的结果执行略有不同的语句块。每个语句块以BEGIN开始，以END结束。

USE AdventureWorks2012;
GO
DECLARE @AvgWeight decimal(8,2), @BikeCount int
IF 
(SELECT COUNT(*) FROM Production.Product WHERE Name LIKE 'Touring-3000%' ) > 5
BEGIN
   SET @BikeCount = 
        (SELECT COUNT(*) 
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%');
   SET @AvgWeight = 
        (SELECT AVG(Weight) 
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%');
   PRINT 'There are ' + CAST(@BikeCount AS varchar(3)) + ' Touring-3000 bikes.'
   PRINT 'The average weight of the top 5 Touring-3000 bikes is ' + CAST(@AvgWeight AS varchar(8)) + '.';
END
ELSE 
BEGIN
SET @AvgWeight = 
        (SELECT AVG(Weight)
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%' );
   PRINT 'Average weight of the Touring-3000 bikes is ' + CAST(@AvgWeight AS varchar(8)) + '.' ;
END ;
GO

使用嵌套IF…其他语句 下面的例子展示了IF…ELSE语句如何嵌套在另一个语句中。将@Number变量设置为5、50和500，以测试每条语句。

DECLARE @Number int
SET @Number = 50
IF @Number > 100
   PRINT 'The number is large.'
ELSE 
   BEGIN
      IF @Number < 10
      PRINT 'The number is small'
   ELSE
      PRINT 'The number is medium'
   END ;
GO

USE AdventureWorks2012;
GO
IF 
(SELECT COUNT(*) FROM Production.Product WHERE Name LIKE 'Touring-3000%' ) > 5
PRINT 'There are more than 5 Touring-3000 bicycles.'
ELSE PRINT 'There are 5 or less Touring-3000 bicycles.' ;
GO

澄清一些逻辑等价解。

if语句

if (a) then b

逻辑上等价于

(!a || b)

这是逻辑等价维基百科文章中涉及条件语句的逻辑等价部分的第一行。

要包含else，您所要做的就是添加另一个条件

if(a) then b; 
if(!a) then c;

哪个在逻辑上是等价的 （！A || b) && (A || c)

以OP为例:

IF IsNumeric(@OrderNumber) = 1
    OrderNumber = @OrderNumber
ELSE
    OrderNumber LIKE '%' + @OrderNumber + '%'

逻辑上等价的是:

(IsNumeric(@OrderNumber) <> 1 OR OrderNumber = @OrderNumber)
AND (IsNumeric(@OrderNumber) = 1 OR OrderNumber LIKE '%' + @OrderNumber + '%' )

If @LstTransDt is Null
                begin
                    Set @OpenQty=0
                end
            else
                begin
                   Select   @OpenQty=IsNull(Sum(ClosingQty),0)  
                   From  ProductAndDepotWiseMonitoring  
                   Where   Pcd=@PCd And PtpCd=@PTpCd And TransDt=@LstTransDt      
                end 

看看这是否有帮助。