[tsql] Select query to remove non-numeric characters

Here's a version which pulls all digits from a string; i.e. given I'm 35 years old; I was born in 1982. The average family has 2.4 children. this would return 35198224. i.e. it's good where you've got numeric data which may have been formatted as a code (e.g. #123,456,789 / 123-00005), but isn't appropriate if you're looking to pull out specific numbers (i.e. as opposed to digits / just the numeric characters) from the text. Also it only handles digits; so won't return negative signs (-) or periods .).

declare @table table (id bigint not null identity (1,1), data nvarchar(max)) 
insert @table (data) 
values ('hello 123 its 45613 then') --outputs: 12345613
,('1 some other string 98 example 4') --outputs: 1984
,('AB ABCDE # 123') --outputs: 123 
,('ABCDE# 123') --outputs: 123
,('AB: ABC# 123') --outputs: 123
; with NonNumerics as (
    select id
    , data original
    --the below line replaces all digits with blanks
    , replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(data,'0',''),'1',''),'2',''),'3',''),'4',''),'5',''),'6',''),'7',''),'8',''),'9','') nonNumeric
    from @table
)
--each iteration of the below CTE removes another non-numeric character from the original string, putting the result into the numerics column
, Numerics as (
    select id
    , replace(original, substring(nonNumeric,1,1), '') numerics
    , replace(nonNumeric, substring(nonNumeric,1,1), '') charsToreplace
    , len(replace(nonNumeric, substring(nonNumeric,1,1), '')) charsRemaining
    from NonNumerics

    union all

    select id
    , replace(numerics, substring(charsToreplace,1,1), '') numerics
    , replace(charsToreplace, substring(charsToreplace,1,1), '') charsToreplace
    , len(replace(charsToreplace, substring(charsToreplace,1,1), '')) charsRemaining
    from Numerics
    where charsRemaining > 0
)
--we select only those strings with `charsRemaining=0`; i.e. the rows for which all non-numeric characters have been removed; there should be 1 row returned for every 1 row in the original data set.
select * from Numerics where charsRemaining = 0

This code works by removing all the digits (i.e. the characters we want) from a the given strings by replacing them with blanks. Then it goes through the original string (which includes the digits) removing all of the characters that were left (i.e. the non-numeric characters), thus leaving only the digits.

The reason we do this in 2 steps, rather than just removing all non-numeric characters in the first place is there are only 10 digits, whilst there are a huge number of possible characters; so replacing that small list is relatively fast; then gives us a list of those non-numeric characters which actually exist in the string, so we can then replace that small set.

The method makes use of recursive SQL, using common table expressions (CTEs).

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Select query to remove non-numeric characters