TSQL Format SSN/TIN (SQL Server 2016+) - sql

Question

I need to format US SSN/TIN strings with dashes when they appear to be valid
(where valid = 9 digits) and otherwise return what is in the field (with leading 0s).
123456789 should format to 123-45-6789
and 3456789 formats to 003-45-6789
Can someone tell me why this code doesn't work?
Declare #TaxIDNum VarChar(11)
Set #TaxIDNum = '3456789'
Set #TaxIDNum = Right('0000'+#TaxIDNum,9)
Set #TaxIDNum =
CASE #TaxIDNum WHEN Len(#TaxIDNum)=9 THEN
CASE #TaxIDNum
WHEN IsNumeric(#TaxIDNum)
THEN Left(#TaxIDNum,3)+'-'+Right(Left(#TaxIDNum,5),2)+'-'+Right(#TaxIDNum,4)
ELSE #TaxIDNum END -- return existing value
ELSE #TaxIDNum END -- return existing value
select #TaxIDNum, len(#TaxIDNum) as Length
I get a red squiggly error on the equals in "=9":
(Error text is: "Incorrect syntax near '='.")
Any solution that both works with a select or set, and solves the problem is welcome.
Thanks to #Larnu for mentioning Set #TaxIDNum=FORMAT(CONVERT(int,#TaxIDNum),'000-00-0000')
If I had error handling (our SSvr install doesn't) I would use Format. However if there is bad data, it breaks my query in a way from which I cannot recover.
Set #TaxIDNum=Replace('123-45-6789','-','') does avoid errors if the only data problem is that some of the rows are already formatted.

Answer 1

Seems like you could use FORMAT:
SELECT FORMAT(CONVERT(int,#TaxIDNum),'000-00-0000');

Answer 2

Why it does not work
From comments by [HABO][1]
You have mixed simple and searched case syntaxes, hence the complaint.
You should use LIKE (learn.microsoft.com/en-us/sql/t-sql/language-elements/…)
with a suitable pattern, e.g.
'[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]', to determine if the
string contains only nine numeric characters.
So I tried this, which also didn't work:
SET #TaxIDNum =
CASE #TaxIDNum Like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'
WHEN true
THEN …
HABO:
You've hit an fiendish edge case.
There is a boolean data type (with
values TRUE, FALSE and UNKNOWN), but you cannot get a firm grip on
one:
"Unlike other SQL Server data types, a Boolean data type cannot
be specified as the data type of a table column or variable, and
cannot be returned in a result set."
You can't have CASE «boolean-expression» WHEN true THEN «result» END
Solution:
Use LIKE leaving the CASE expression empty
declare #TaxIDNum VarChar(11)
set #TaxIDNum='3456789'
set #TaxIDNum=right('0000'+#TaxIDNum,9)
select #TaxIDNum
SET #TaxIDNum = CASE
WHEN #TaxIDNum Like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'
THEN Left(#TaxIDNum,3)+'-'+SubString(#TaxIDNum,4,2)+'-'+Right(#TaxIDNum,4)
ELSE #TaxIDNum END
select #TaxIDNum