Why isn't “String or Binary data would be truncated” a more descriptive error?

Question

To start: I understand what this error means - I\'m not attempting to resolve an instance of it.

This error is notoriously difficult to troubleshoot

Answer 1

Answering a DUP that got closed, so answering here instead. This pattern can be used, if somewhat elaborate, but it can be useful when it is not trivial to change the application, or set up profiler to see what is happening. Sometimes, you just need the error to propagate to the APP itself so you can see right from the APP, the correct and useful error message.

In those cases, a quick poke into the DB with this solution will save you lots of time. Save it as a template, and make quick changes to it to solve this problem on any table.

The problem

Sample table

create table StringTruncation
(A int, B varchar(10), C nvarchar(5), D nvarchar(max), E datetime)

Sample statement

insert StringTruncation values
(1, '0123456789', 'abcdef', 'This overflows on C', GETDATE())

The dreaded useless error

Msg 8152, Level 16, State 4, Line 1
String or binary data would be truncated.
The statement has been terminated.

The example shows only 2 columns where it could overflow, but imagine if it were 20 columns, or 40.

The solution

-- First move the table out of the way
exec sp_rename StringTruncation, StringTruncation_;

-- cover it with a query
create view dbo.StringTruncation
with schemabinding
as
select
    A,
    convert(Nvarchar(max),B) B,
    convert(Nvarchar(max),C) C,
    D, E
from dbo.StringTruncation_
GO

-- use a trigger to allow INSERTs, with the length checks thrown in
create trigger dbo.trig_ioi_StringTruncation
on StringTruncation
instead of insert
as
set nocount on
declare @offending nvarchar(max)
select TOP 1 @offending = case
    when len(C) > 5 then 'Data too long for Column [C] Size 5: ' + C
    when len(B) > 10 then 'Data too long for Column [D] Size 10: ' + B
    end
from inserted
where len(C) > 5 or len(B) > 10
GO

-- keep good data
if @@rowcount = 0
    insert StringTruncation_
    select * from inserted
else
    raiserror(@offending,16,1)
GO

Test it

insert StringTruncation values
(1, '0s123456789', 'abcde', 'This overflows on C', GETDATE())

Result

Msg 50000, Level 16, State 1, Procedure trig_ioi_StringTruncation, Line 18
Data too long for Column [D] Size 10: 0s123456789

(1 row(s) affected)

Notes

• It needs a mirror trigger for UPDATEs
• It will currently only report on the first offending record-column. It is possible to report more than one record-column, but I believe that is actually counter-productive.