设置非数字，因为它们进入 null

Question

I have a paymentHistory field that is an int that tracks how many payments have been made from the account before. I have a source that is varchar for this field and someone enters 1.11 by accident on the front end. I can't change my source but I want to be able to allow only numeric and convert the non-numeric to null values. Can someone please give an example how I would convert values in this PaymentHistory column to only numeric or null. Thanks!

Answer 1

You can reject non-numeric values with a check constraint:

alter table chk_paymenthistory add constraint chk_paymenthistory_num
    check (num not like '%[^0-9]%');

This only allows digits into the column. But you don't want to reject the value, you want to replace it with NULL .

If you are inserting the rows using insert , you can use try_cast() / try_convert() :

insert into paymenthistory ( . . . )
    values ( . . ., try_cast(num as int), . . .);

This will convert the value to an integer (and you could use bigint or numeric instead). It will then be saved as a string -- but will be null if it is not a valid number.

That leaves you with a trigger for other situations. But what other situation? What comes to mind is bulk insert , but that doesn't invoke triggers by default. You can turn them on, if you want this functionality.