Error 360: Cannot modify table or view used in subquery

INFORMIX-SE 7.32:

I'm getting error 360 when I try to execute the following statement:

update transaction
   set transaction.colx = (select tab1.cola from tab1)
 where transaction.num  = (select max(transaction.num) from transa开发者_StackOverflowction)
   and transaction.colx IS NULL;

Any ideas?

You're trying to UPDATE the table transaction and read from the same table using SELECT MAX with the same query. You cannot do that.

Subquery restrictions

In general, you cannot modify a table and select from the same table in a subquery. For example, this limitation applies to statements of the following forms:
DELETE FROM t WHERE ... (SELECT ... FROM t ...);
UPDATE t ... WHERE col = (SELECT ... FROM t ...);
{INSERT|REPLACE} INTO t (SELECT ... FROM t ...);