SQL UPDATE specific characters in string

Use this,

DECLARE @MyString VARCHAR(30) = '20150223-0000000001'

SELECT STUFF(@MyString,CHARINDEX('-',@MyString)+1,2,'AB')

If there is a lot of data, you could consider to use .WRITE clause. But it is limited to VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX) data types.

If you have one of the following column types, the .WRITE clause is easiest for this purpose, example below:

UPDATE Codes
SET val.WRITE('AB',9,2)
GO

Other possible choice could be simple REPLACE:

UPDATE Codes
SET val=REPLACE(val,SUBSTRING(val,10,2),'AB')
GO

or STUFF:

UPDATE Codes
SET val=STUFF(val,10,2,'AB')
GO

I based on the information that there is always 8 characters of date and one dash after in the column. I prepered a table and checked some solutions which were mentioned here.

CREATE TABLE Codes(val NVARCHAR(MAX))

INSERT INTO Codes
SELECT TOP 500000 CONVERT(NVARCHAR(128),GETDATE()-CHECKSUM(NEWID())%1000,112)+'-00'+CAST(ABS(CAST(CHECKSUM(NEWID())%10000 AS INT)) AS NVARCHAR(128))
FROM sys.columns s1 CROSS JOIN sys.columns s2

I run some tests, and based on 10kk rows with NVARCHAR(MAX) column, I got following results:

+---------+------------+
| Method  |    Time    |
+---------+------------+
| .WRITE  | 28 seconds |
| REPLACE | 30 seconds |
| STUFF   | 15 seconds |
+---------+------------+

As we can see STUFF looks like the best option for updating part of string. .WRITE should be consider when you insert or append new data into string, then you could take advantage of minimall logging if the database recovery model is set to bulk-logged or simple. According to MSDN articleabout UPDATE statement: Updating Large Value Data Types

According to the OP Comment:-

Its always 8 charachters before the dash but the characters after the dash can vary. It has to update the first two after the dash.

use the next simple code:-

DECLARE @MyString VARCHAR(30) = '20150223-0000000001'

SELECT REPLACE(@MyString,SUBSTRING(@MyString,9,3),'-AB')

Result:-

20150223-AB00000001

try,

update table set column=stuff(column,charindex('-',column)+1,2,'AB')

Declare @Table1 TABLE (DateValue Varchar(50))
INSERT INTO @Table1
SELECT '20150223-000000001' Union all
SELECT '20150224-000000002' Union all
SELECT '20150225-000000003'

SELECT DateValue,
CONCAT(SUBSTRING(DateValue,0,CHARINDEX('-',DateValue)),
REPLACE(LEFT(SUBSTRING(DateValue,CHARINDEX('-',DateValue)+1,Len(DateValue)),2),'00','-AB'),
SUBSTRING(DateValue,CHARINDEX('-',DateValue)+1,Len(DateValue))) AS ExpectedDateValue
FROM @Table1

OutPut

   DateValue                ExpectedDateValue
---------------------------------------------
   20150223-000000001   20150223-AB000000001
   20150224-000000002   20150224-AB000000002
   20150225-000000003   20150225-AB000000003

To Update

Update @Table1
SEt DateValue= CONCAT(SUBSTRING(DateValue,0,CHARINDEX('-',DateValue)),
REPLACE(LEFT(SUBSTRING(DateValue,CHARINDEX('-',DateValue)+1,Len(DateValue)),2),'00','-AB'),
SUBSTRING(DateValue,CHARINDEX('-',DateValue)+1,Len(DateValue)))
From @Table1

SELECT * from @Table1

OutPut

    DateValue
   -------------
20150223-AB000000001
20150224-AB000000002
20150225-AB000000003