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?

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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 ...);