SQL - Add new column with outputs as values - sql-server

Question

Just wondering how I might go about adding the ouputted results as a new column to an exsisting table.
What I'm tryng to do is extract the date from a string which is in another column. I have the below code to do this:
Code
CREATE FUNCTION dbo.udf_GetNumeric
(
#strAlphaNumeric VARCHAR(256)
)
RETURNS VARCHAR(256)
AS
BEGIN
DECLARE #intAlpha INT
SET #intAlpha = PATINDEX('%[^0-9]%', #strAlphaNumeric)
BEGIN
WHILE #intAlpha > 0
BEGIN
SET #strAlphaNumeric = STUFF(#strAlphaNumeric, #intAlpha, 1, '' )
SET #intAlpha = PATINDEX('%[^0-9]%', #strAlphaNumeric )
END
END
RETURN ISNULL(#strAlphaNumeric,0)
END
GO
Now use the function as
SELECT dbo.udf_GetNumeric(column_name)
from table_name
The issue is that I want the result to be placed in a new column in an exsisting table. I have tried the below code but no luck.
ALTER TABLE [Data_Cube_Data].[dbo].[DB_Test]
ADD reportDated nvarchar NULL;
insert into [DB].[dbo].[DB_Test](reportDate)
SELECT
(SELECT dbo.udf_GetNumeric(FileNamewithDate) from [DB].[dbo].[DB_Test])

Answer 1

The syntax should be an UPDATE, not an INSERT, because you want to update existing rows, not insert new ones:
UPDATE Data_Cube_Data.dbo.DB_Test -- you don't need square bracket noise
SET reportDate = dbo.udf_GetNumeric(FileNamewithDate);
But yeah, I agree with the others, the function looks like the result of a "how can I make this object the least efficient thing in my entire database?" contest. Here's a better alternative:
-- better, set-based TVF with no while loop
CREATE FUNCTION dbo.tvf_GetNumeric
(#strAlphaNumeric varchar(256))
RETURNS TABLE
AS
RETURN
(
WITH cte(n) AS
(
SELECT TOP (256) n = ROW_NUMBER() OVER (ORDER BY ##SPID)
FROM sys.all_objects
)
SELECT output = COALESCE(STRING_AGG(
SUBSTRING(#strAlphaNumeric, n, 1), '')
WITHIN GROUP (ORDER BY n), '')
FROM cte
WHERE SUBSTRING(#strAlphaNumeric, n, 1) LIKE '%[0-9]%'
);
Then the query is:
UPDATE t
SET t.reportDate = tvf.output
FROM dbo.DB_Test AS t
CROSS APPLY dbo.tvf_GetNumeric(t.FileNamewithDate) AS tvf;
Example db<>fiddle that shows this has the same behavior as your existing function.

Answer 2

The function
As i mentioned in the comments, I would strongly suggest rewriting the function, it'll perform terribly. Multi-line table value function can perform poorly, and you also have a WHILE which will perform awfully. SQL is a set based language, and so you should be using set based methods.
There are a couple of alternatives though:
Inlinable Scalar Function
SQL Server 2019 can inline function, so you could inline the above. I do, however, assume that your value can only contain the characters A-z and 0-9. if it can contain other characters, such as periods (.), commas (,), quotes (") or even white space ( ), or your not on 2019 then don't use this:
CREATE OR ALTER FUNCTION dbo.udf_GetNumeric (#strAlphaNumeric varchar(256))
RETURNS varchar(256) AS
BEGIN
RETURN TRY_CONVERT(int,REPLACE(TRANSLATE(LOWER(#strAlphaNumeric),'abcdefghigclmnopqrstuvwxyz',REPLICATE('|',26)),'|',''));
END;
GO
SELECT dbo.udf_GetNumeric('abs132hjsdf');
The LOWER is there in case you are using a case sensitive collation.
Inline Table Value Function
This is the better solution in my mind, and doesn't have the caveats of the above.
It uses a Tally to split the data into individual characters, and then only reaggregate the characters that are a digit. Note that I assume you are using SQL Server 2017+ here:
DROP FUNCTION udf_GetNumeric; --Need to drop as it's a scalar function at the moment
GO
CREATE OR ALTER FUNCTION dbo.udf_GetNumeric (#strAlphaNumeric varchar(256))
RETURNS table AS
RETURN
WITH N AS (
SELECT N
FROM (VALUES(NULL),(NULL),(NULL),(NULL)) N(N)),
Tally AS(
SELECT TOP (LEN(#strAlphaNumeric))
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
FROM N N1, N N2, N N3, N N4)
SELECT STRING_AGG(CASE WHEN V.C LIKE '[0-9]' THEN V.C END,'') WITHIN GROUP (ORDER BY T.I) AS strNumeric
FROM Tally T
CROSS APPLY (VALUES(SUBSTRING(#strAlphaNumeric,T.I,1)))V(C);
GO
SELECT *
FROM dbo.udf_GetNumeric('abs132hjsdf');
Your table
You define reportDated as nvarchar; this means nvarchar(1). Your function, however, returns a varchar(256); this will rarely fit in an nvarchar(1).
Define the column properly:
ALTER TABLE [dbo].[DB_Test] ADD reportDated varchar(256) NULL;
If you've already created the column then do the following:
ALTER TABLE [dbo].[DB_Test] ALTER COLUMN reportDated varchar(256) NULL;
I note, however, that the column is called "dated", which implies a date value, but it's a (n)varchar; that sounds like a flaw.
Updating the column
Use an UPDATE statement. Depending on the solution this would one of the following:
--Scalar function
UPDATE [dbo].[DB_Test]
SET reportDated = dbo.udf_GetNumeric(FileNamewithDate);
--Table Value Function
UPDATE DBT
SET reportDated = GN.strNumeric
FROM [dbo].[DB_Test] DBT
CROSS APPLY dbo.udf_GetNumeric(FileNamewithDate);