[sql] Better techniques for trimming leading zeros in SQL Server?

I've been using this for some time:

SUBSTRING(str_col, PATINDEX('%[^0]%', str_col), LEN(str_col))

However recently, I've found a problem with columns with all "0" characters like '00000000' because it never finds a non-"0" character to match.

An alternative technique I've seen is to use TRIM:

REPLACE(LTRIM(REPLACE(str_col, '0', ' ')), ' ', '0')

This has a problem if there are embedded spaces, because they will be turned into "0"s when the spaces are turned back into "0"s.

I'm trying to avoid a scalar UDF. I've found a lot of performance problems with UDFs in SQL Server 2005.

In MySQL you can do this...

Trim(Leading '0' from your_column)

  SUBSTRING(str_col, IIF(LEN(str_col) > 0, PATINDEX('%[^0]%', LEFT(str_col, LEN(str_col) - 1) + '.'), 0), LEN(str_col))

Works fine even with '0', '00' and so on.

If you do not want to convert into int, I prefer this below logic because it can handle nulls IFNULL(field,LTRIM(field,'0'))

Why don't you just cast the value to INTEGER and then back to VARCHAR?

SELECT  CAST(CAST('000000000' AS INTEGER) AS VARCHAR)

--------
       0

For converting number as varchar to int, you could also use simple

(column + 0)

The following will return '0' if the string consists entirely of zeros:

CASE WHEN SUBSTRING(str_col, PATINDEX('%[^0]%', str_col+'.'), LEN(str_col)) = '' THEN '0' ELSE SUBSTRING(str_col, PATINDEX('%[^0]%', str_col+'.'), LEN(str_col)) END AS str_col

cast(value as int) will always work if string is a number

Instead of a space replace the 0's with a 'rare' whitespace character that shouldn't normally be in the column's text. A line feed is probably good enough for a column like this. Then you can LTrim normally and replace the special character with 0's again.

Other answers here to not take into consideration if you have all-zero's (or even a single zero).
Some always default an empty string to zero, which is wrong when it is supposed to remain blank.
Re-read the original question. This answers what the Questioner wants.

Solution #1:

--This example uses both Leading and Trailing zero's.
--Avoid losing those Trailing zero's and converting embedded spaces into more zeros.
--I added a non-whitespace character ("_") to retain trailing zero's after calling Replace().
--Simply remove the RTrim() function call if you want to preserve trailing spaces.
--If you treat zero's and empty-strings as the same thing for your application,
--  then you may skip the Case-Statement entirely and just use CN.CleanNumber .
DECLARE @WackadooNumber VarChar(50) = ' 0 0123ABC D0 '--'000'--
SELECT WN.WackadooNumber, CN.CleanNumber,
       (CASE WHEN WN.WackadooNumber LIKE '%0%' AND CN.CleanNumber = '' THEN '0' ELSE CN.CleanNumber END)[AllowZero]
 FROM (SELECT @WackadooNumber[WackadooNumber]) AS WN
 OUTER APPLY (SELECT RTRIM(RIGHT(WN.WackadooNumber, LEN(LTRIM(REPLACE(WN.WackadooNumber + '_', '0', ' '))) - 1))[CleanNumber]) AS CN
--Result: "123ABC D0"

Solution #2 (with sample data):

SELECT O.Type, O.Value, Parsed.Value[WrongValue],
       (CASE WHEN CHARINDEX('0', T.Value)  > 0--If there's at least one zero.
              AND LEN(Parsed.Value) = 0--And the trimmed length is zero.
             THEN '0' ELSE Parsed.Value END)[FinalValue],
       (CASE WHEN CHARINDEX('0', T.Value)  > 0--If there's at least one zero.
              AND LEN(Parsed.TrimmedValue) = 0--And the trimmed length is zero.
             THEN '0' ELSE LTRIM(RTRIM(Parsed.TrimmedValue)) END)[FinalTrimmedValue]
  FROM 
  (
    VALUES ('Null', NULL), ('EmptyString', ''),
           ('Zero', '0'), ('Zero', '0000'), ('Zero', '000.000'),
           ('Spaces', '    0   A B C '), ('Number', '000123'),
           ('AlphaNum', '000ABC123'), ('NoZero', 'NoZerosHere')
  ) AS O(Type, Value)--O is for Original.
  CROSS APPLY
  ( --This Step is Optional.  Use if you also want to remove leading spaces.
    SELECT LTRIM(RTRIM(O.Value))[Value]
  ) AS T--T is for Trimmed.
  CROSS APPLY
  ( --From @CadeRoux's Post.
    SELECT SUBSTRING(O.Value, PATINDEX('%[^0]%', O.Value + '.'), LEN(O.Value))[Value],
           SUBSTRING(T.Value, PATINDEX('%[^0]%', T.Value + '.'), LEN(T.Value))[TrimmedValue]
  ) AS Parsed

Results:

Summary:

You could use what I have above for a one-off removal of leading-zero's.
If you plan on reusing it a lot, then place it in an Inline-Table-Valued-Function (ITVF).
Your concerns about performance problems with UDF's is understandable.
However, this problem only applies to All-Scalar-Functions and Multi-Statement-Table-Functions.
Using ITVF's is perfectly fine.

I have the same problem with our 3rd-Party database.
With Alpha-Numeric fields many are entered in without the leading spaces, dang humans!
This makes joins impossible without cleaning up the missing leading-zeros.

Conclusion:

Instead of removing the leading-zeros, you may want to consider just padding your trimmed-values with leading-zeros when you do your joins.
Better yet, clean up your data in the table by adding leading zeros, then rebuilding your indexes.
I think this would be WAY faster and less complex.

SELECT RIGHT('0000000000' + LTRIM(RTRIM(NULLIF(' 0A10  ', ''))), 10)--0000000A10
SELECT RIGHT('0000000000' + LTRIM(RTRIM(NULLIF('', ''))), 10)--NULL --When Blank.

If you are using Snowflake SQL, might use this:

ltrim(str_col,'0')

The ltrim function removes all instances of the designated set of characters from the left side.

So ltrim(str_col,'0') on '00000008A' would return '8A'

And rtrim(str_col,'0.') on '$125.00' would return '$125'

replace(ltrim(replace(Fieldname.TableName, '0', '')), '', '0')

The suggestion from Thomas G worked for our needs.

The field in our case was already string and only the leading zeros needed to be trimmed. Mostly it's all numeric but sometimes there are letters so the previous INT conversion would crash.

My version of this is an adaptation of Arvo's work, with a little more added on to ensure two other cases.

1) If we have all 0s, we should return the digit 0.

2) If we have a blank, we should still return a blank character.

CASE 
    WHEN PATINDEX('%[^0]%', str_col + '.') > LEN(str_col) THEN RIGHT(str_col, 1) 
    ELSE SUBSTRING(str_col, PATINDEX('%[^0]%', str_col + '.'), LEN(str_col))
 END

This makes a nice Function....

DROP FUNCTION [dbo].[FN_StripLeading]
GO
CREATE FUNCTION [dbo].[FN_StripLeading] (@string VarChar(128), @stripChar VarChar(1))
RETURNS VarChar(128)
AS
BEGIN
-- http://stackoverflow.com/questions/662383/better-techniques-for-trimming-leading-zeros-in-sql-server
    DECLARE @retVal VarChar(128),
            @pattern varChar(10)
    SELECT @pattern = '%[^'+@stripChar+']%'
    SELECT @retVal = CASE WHEN SUBSTRING(@string, PATINDEX(@pattern, @string+'.'), LEN(@string)) = '' THEN @stripChar ELSE SUBSTRING(@string, PATINDEX(@pattern, @string+'.'), LEN(@string)) END
    RETURN (@retVal)
END
GO
GRANT EXECUTE ON [dbo].[FN_StripLeading] TO PUBLIC

Try this:

replace(ltrim(replace(@str, '0', ' ')), ' ', '0')

This might help

SELECT ABS(column_name) FROM [db].[schema].[table]

SELECT CAST(CAST('000000000' AS INTEGER) AS VARCHAR)

This has a limit on the length of the string that can be converted to an INT