Changing Values in T-SQL–#SQLNewBlogger

Another post for me that is simple and hopefully serves as an example for people trying to get blogging as #SQLNewBloggers.

Recently I ran across a question posted by a beginner on the Internet and thought this would be a good, basic topic to cover. The question was: how can I replace a value in a comma separated string in a table?

This post covers the basics of this task.

Scenario

Suppose you have some strings in a table, and they contain multiple values. I see this often when application developers serialize some data. For example, I might create a table like this:

CREATE TABLE mytable
(   mykey INT NOT NULL CONSTRAINT mytablepk PRIMARY KEY
   , myval VARCHAR(100));
GO
INSERT dbo.mytable
     (mykey, myval)
VALUES
     (1, 'apple,pear,banana')
   , (2, 'pear,peach,melon');
GO
SELECT * FROM dbo.mytable AS m;

This has a few rows of multiple values in a field.

Imagine now I need to change pear to grape in all rows. I want a simple solution to do this.

Solution

I have seen some people try to use complex substring calls paired with other functions to do this, but T-SQL gives you a really simple solution. We have a REPLACE() function that allows us to change a string without parsing it.

The simple way to do this is like this:

SELECT
      m.mykey
    , m.myval
    , REPLACE(m.myval, 'pear', 'grape') AS newstring
FROM dbo.mytable AS m;

Always run a SELECT before an UPDATE, but in this case, I can see that pear has been removed and grape is in its place.

REPLACE() works by passing in a string as the first parameter, then a second string to search for, pear in this case, and finally a replacement. I could then put together an UPDATE statement to change my table.

UPDATE dbo.mytable
  SET myval = REPLACE(myval, 'pear', 'grape')
FROM dbo.mytable AS m;

If I run this, the results shown above for newstring will replace the myval string for all rows.

SQLNewBlogger

This is an example of a basic type of T-SQL solution that is simple, with a quick explanation. I answered this for someone and then spent 10 minutes writing this up.

A good story to have ready for an interview.