SQL Server迁移时计算列IF语法报错问题求助

SAP将停用原有SQL环境，我正在开发迁移工具将数据转至SQL Server。创建包含计算列的A_Invoices表时，SQL Server报错：

Incorrect syntax near the keyword 'if'

修改数据类型后的建表语句如下：

CREATE TABLE A_Invoices
(
    Invoice_ID int NOT NULL IDENTITY(1,1) PRIMARY KEY, 
    Invoice_No int, 
    Type varchar(2), 
    Invoice_Date date, 
    Transaction_Date date DEFAULT GETDATE(), 
    Customer_ID int, 
    Customer_Name varchar(100), 
    Nominal_ID int, 
    Add1 varchar(100), 
    Add2 varchar(200), 
    City varchar(100), 
    State varchar(2), 
    Zip varchar(15), 
    Terms varchar(100), 
    Amount_Net float, 
    Amount_Tax float, 
    Amount_Gross float, 
    Tax_Rate float(53), 
    Tax_Code varchar(2), 
    Settlement_Due_Days int, 
    Settlement_Discount_Rate float(53) DEFAULT 0.0, 
    Settlement_Discount_Amount AS 
        IF "Settlement_Discount_Rate" > 0 
           THEN ("Amount_Net"*"Settlement_Discount_Rate") / 100 
           ELSE 0.0 
        ENDIF, 
    Printed varchar(1) DEFAULT 'N', 
    Posted varchar(1) DEFAULT 'N', 
    Flag_Prepayment varchar(1) DEFAULT 'N', 
    Prepayment_Months int DEFAULT 0, 
    Prepayment_Amount float DEFAULT 0.0, 
    Flag_Deposit varchar(1) DEFAULT 'N', 
    Flag_Ad_Hoc varchar(1) DEFAULT 'N', 
    Customer_Order_No varchar(50), 
    Details varchar(100), 
    Pay_Due_Days int DEFAULT 0, 
    Open_Editing int DEFAULT 0, 
    Editing_Name varchar(100) DEFAULT 'System', 
    Updated_Name varchar(100) DEFAULT 'System', 
    Updated DateTime2 DEFAULT GETDATE()
);

更新说明 #

语句中的双引号来自SQL Anywhere的查询语句，多数表由早期版本SQL Anywhere升级而来，对应的元数据查询语句如下：

SELECT c.column_name AS 'Name', 
c.base_type_str AS 'Type',
c.nulls AS 'Nulls', 
c.`default` AS 'Default' 
FROM systabcol c KEY JOIN systab t ON t.table_name = 'vTB' 

解决办法 #

目前问题已解决，针对IF语法的转换处理代码如下：

If vComputed = "C" Then
vMSComputed = "Y"
If vDefault.Contains("if") Then
    Dim s As New System.Text.StringBuilder(vDefault)
    s.Replace("if", "CASE WHEN", 0, 2)
    s.Replace("endif", "END", 0, s.Length)
    s.Replace("""", "")
    vMSDefault = s.ToString

End If
Else
vMSComputed = "N"
End If

另外，针对创建表时提示表已存在的问题，使用以下语句判断后再执行建表操作：

IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'vTable')

内容的提问来源于stack exchange，提问作者gchq