FROM statement using source data that's known to have flaws. Back to the OP - either filter out the bad records in the WHERE clause, or put a CASE statement in the UPDATE list. No need for a cursor.

Modifies a column's values in existing rows of a table or view. Restriction: You cannot use UPDATE on a table accessed via an engine that does not support UPDATE processing. You can update one or more ...

The following example grants UPDATE and INSERT authority to user TESTUSER on the Oracle Rdb table ORDERS. Because the CONNECT statement is omitted, an implicit connection, that uses the default ...