Need help converting to bigint

Question

HI,
I need to update a field based on 3 string concatenated together that need to be converted to a bigint:
SET
ReferenceNumber =
CAST(CONVERT(varchar(10),
CheckDate, 112)
+ string1+ string2
as
bigint)
string 1 and string 2 are numbers with leading zeros
I have tried many different syntax but getting the arithmetic overflow error converting to bigint
Any Idea why?

Answer 1

Please follow basic Netiquette and post the DDL we need to answer this. Follow industry and ANSI/ISO standards in your data. You should follow ISO-11179 rules for naming data elements. You should follow ISO-8601 rules for displaying temporal data. We need
to know the data types, keys and constraints on the table. Avoid dialect in favor of ANSI/ISO Standard SQL. 
>> I need to update a field [sic] based on 3 string concatenated together that need to be converted to a BIGINT: <<
Columns are not fields; this is a fundamental concept in RDBMS. Why are you using BIGINT? What math are you doing on it? What math do you have that requires a number greater than the atoms in the Universe? 
You do not understand  that SQL is a database language, so you treat it like COBOL, or VB or whatever you learned first. That mindset is why you said “field”! Think in terms of  data, not computations and concatenations. 
If you want to locate something in time and some kind of space, why not use three columns? My guess, since you did not bother with DDL or even sample data, is this: 
CREATE TABLE Foobar
 check_date DATE DEFAULT CURRENT_TIMESTAMP NOT NULL,
 string_1 CHAR(5) NOT NULL
   CHECK (string_1 LIKE '[0-9][0-9][0-9][0-9][0-9][0-9]'),
 string_2 CHAR(5) NOT NULL
   CHECK (string_2 LIKE '[0-9][0-9][0-9][0-9][0-9][0-9]'),
 UNIQUE (check_date, string_1 , string_2),
If you wish, you can add a computed column with the concatenation, but I would tend to think it belongs in a VIEW or query. 
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