Hi,
as far as I know, the only statements you are entitled to execute in an informix trigger are events declarations, SQL Statements or invokea stored procedure.
I guess your code example is not real, because there is no point in using a trigger to define a variable an assign it a value. The purpose of a trigger is precisely to automatically trigger an SQL "edit" statement ( ie INSERT, UPDATE or DELETE ) fired by another SQL statement under certain conditions.
If you want to use more elaborate code than a simple SQL statement, create the relevant stored procedure, and invoke it from the trigger code as "EXECUTE PROCEDURE yourprocedure(your parameters)"
Best regards,
Eric