Can I use SQL (in an AS400 environment) to update a substring of a field?

In this example, the update to the substring is conditional.

Follows is the SQL syntax I used and the error message I received:


update a04bsydtaa/bsyglgp set substr (lggl#,5,4) = '0010' where lghsp# = 999


Token ( was not valid. Valid tokens: =.