SQL 查询将 varchar 转换为日期时间

Question

SELECT distinct 
    (Client_Name),
    AMC_Expiry as date,
    Dealer_Name,
    Location,
    Product_Type, Product_Name,
    Quantity, 
    Install_Date, Warranty_Expiry, AMC_Expiry,
    mail_sent,
    billing_by, callhandled_by   
FROM 
     amc 
WHERE   
    (datediff(day, cast(convert(datetime, AMC_Expiry, 103) as datetime),  
                   cast(convert(datetime, GETDATE(), 103) as datetime)) > '-30'   
    and datediff(day, cast(convert(datetime, AMC_Expiry, 103) as datetime),
                      cast(convert(datetime, GETDATE(), 103) as datetime))  < 1)     
    and mail_sent = 'N'   
    or (datediff(day, cast(convert(datetime, Warranty_Expiry, 103) as datetime),
                      cast(convert(datetime, GETDATE(), 103) as datetime)) > '-30'
    and datediff(day, cast(convert(datetime, Warranty_Expiry, 103) as datetime),
                      cast(convert(datetime, GETDATE(), 103) as datetime))  < 1) 
    and mail_sent = 'N'

Answer 1

First, you seem to misunderstand select distinct . DISTINCT is not a function. It is part of a clause that applies to all columns.

Second, you are doing absurd things like:

cast(convert(datetime,GETDATE(),103) as datetime))

Why would you be taking a datetime value, converting it to a datetime and then re-convert it to a datetime .

In addition, you have a comma in the WHERE clause, which makes no sense. And, you have integer constants in single quotes.

Your query has more problems than the one you mention.