Regex pattern inside SQL Replace function?

Question

SELECT REPLACE(\'100.00 GB\', \'%^(^-?\\d*\\.{0,1}\\d+$)%\', \'\');

I want to replace any markup between two

Answer 1

In a general sense, SQL Server does not support regular expressions and you cannot use them in the native T-SQL code.

You could write a CLR function to do that. See here, for example.

Answer 2

For those looking for a performant and easy solution and are willing to enable CLR:

create database TestSQLFunctions
go
use TestSQLFunctions
go
alter database TestSQLFunctions set trustworthy on

EXEC sp_configure 'clr enabled', 1
RECONFIGURE WITH OVERRIDE
go

CREATE ASSEMBLY [SQLFunctions]
AUTHORIZATION [dbo]
FROM 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WITH PERMISSION_SET = SAFE

go

CREATE FUNCTION RegexReplace(
    @input nvarchar(max),
    @pattern nvarchar(max),
    @replacement nvarchar(max)
) RETURNS nvarchar  (max)
AS EXTERNAL NAME SQLFunctions.[SQLFunctions.Regex].Replace; 

go

-- outputs This is a test 
select dbo.RegexReplace('This is a test 12345','[0-9]','')

Content of the DLL:

Answer 3

If you are doing this just for a parameter coming into a Stored Procedure, you can use the following:

declare @badIndex int
set @badIndex = PatIndex('%[^0-9]%', @Param)
while @badIndex > 0
    set @Param = Replace(@Param, Substring(@Param, @badIndex, 1), '')
    set @badIndex = PatIndex('%[^0-9]%', @Param)

Answer 4

You can use PATINDEX to find the first index of the pattern (string's) occurrence. Then use STUFF to stuff another string into the pattern(string) matched.

Loop through each row. Replace each illegal characters with what you want. In your case replace non numeric with blank. The inner loop is if you have more than one illegal character in a current cell that of the loop.

DECLARE @counter int

SET @counter = 0

WHILE(@counter < (SELECT MAX(ID_COLUMN) FROM Table))
BEGIN  

    WHILE 1 = 1
    BEGIN
        DECLARE @RetVal varchar(50)

        SET @RetVal =  (SELECT Column = STUFF(Column, PATINDEX('%[^0-9.]%', Column),1, '')
        FROM Table
        WHERE ID_COLUMN = @counter)

        IF(@RetVal IS NOT NULL)       
          UPDATE Table SET
          Column = @RetVal
          WHERE ID_COLUMN = @counter
        ELSE
            break
    END

    SET @counter = @counter + 1
END

Caution: This is slow though! Having a varchar column may impact. So using LTRIM RTRIM may help a bit. Regardless, it is slow.

Credit goes to this StackOverFlow answer.

EDIT Credit also goes to @srutzky

Edit (by @Tmdean) Instead of doing one row at a time, this answer can be adapted to a more set-based solution. It still iterates the max of the number of non-numeric characters in a single row, so it's not ideal, but I think it should be acceptable in most situations.

WHILE 1 = 1 BEGIN
    WITH q AS
        (SELECT ID_Column, PATINDEX('%[^0-9.]%', Column) AS n
        FROM Table)
    UPDATE Table
    SET Column = STUFF(Column, q.n, 1, '')
    FROM q
    WHERE Table.ID_Column = q.ID_Column AND q.n != 0;

    IF @@ROWCOUNT = 0 BREAK;
END;

You can also improve efficiency quite a lot if you maintain a bit column in the table that indicates whether the field has been scrubbed yet. (NULL represents "Unknown" in my example and should be the column default.)

DECLARE @done bit = 0;
WHILE @done = 0 BEGIN
    WITH q AS
        (SELECT ID_Column, PATINDEX('%[^0-9.]%', Column) AS n
        FROM Table
        WHERE COALESCE(Scrubbed_Column, 0) = 0)
    UPDATE Table
    SET Column = STUFF(Column, q.n, 1, ''),
        Scrubbed_Column = 0
    FROM q
    WHERE Table.ID_Column = q.ID_Column AND q.n != 0;

    IF @@ROWCOUNT = 0 SET @done = 1;

    -- if Scrubbed_Column is still NULL, then the PATINDEX
    -- must have given 0
    UPDATE table
    SET Scrubbed_Column = CASE
        WHEN Scrubbed_Column IS NULL THEN 1
        ELSE NULLIF(Scrubbed_Column, 0)
    END;
END;

If you don't want to change your schema, this is easy to adapt to store intermediate results in a table valued variable which gets applied to the actual table at the end.