First, using phpMyAdmin or the mysql command line, try the query:
SELECT * FROM db WHERE field LIKE 'Song%';
This will show you the records that the query will update. If it doesn't return any records, then the table name, field name, or value to find is wrong.
Assuming the above works, I suspect you're running into a problem with the replacement string not exactly matching what is in the databases. It's going to be difficult to handle because of the embedded line feeds and, possibly, embedded spaces that aren't obvious.
You could do something like:
UPDATE db SET field=REPLACE('src="webpage"', 'id="webpage"', field) WHERE field LIKE 'Song%';
The above won't remove the Adsense code, but will make it inert.