Updating or deleting rows with self-referential subqueries

I'm well aware of the fact that Informix is unable to perform an update or a delete statement if it contains a subquery that refers back to the table that is being updated or deleted. The universal work-around that I've seen in the manuals and posted here is to select the sub-query into a temp table, and then perform the update or delete based on the contents of that temp table. The problem with that is, it breaks up the SQL into multiple statements. Other threads can modify the data between the time of the select and the update or delete. In our case the subquery may not necessarily refer to the row being updated, but instead to (for instance) the max value of one of the columns of the table. How might one set up isolation and locking to allow the select...into temp and the update or delete to occur as if it had been one single SQL statement? Also, if selecting into a temp table and then updating or deleting in these instances is so widely considered the work-around, why doesn't Informix implicitly do this as one operation when it encounters this type of syntax? That way, no other thread could interfere between those two operations? I believe this is what Oracle and SQL Server are doing, because they are able to handle this syntax without a problem. Complicating matters further, we're trying to keep our code as portable as possible, so altering code dramatically to facilitate Informix is not an option here. --John Bejarano, Macromedia, Inc.