[ale] Help with a search and replace in mysql?

[david w. millians]

Okay, I'm trying to fix a database issue. I have a table:
users
with fields
last, first, etc.
Of interest is the field system_num. In the old system, this was the ID 
field from another table, that pointed to the proper value. In the new 
system, that ID field is the proper value.
So how do I do a search and replace? I did RTFM somewhat and discovered 
the replace function. It did replace, but also had the unintended 
consequence of messing things up since the replace is not for the whole 
field but is instead for any matching string in the field.

How do you do this for the whole field?