Restrictions for the compute clause.
You cannot use more than 127 aggregate columns in a compute clause.
You cannot use a compute clause in a cursor declaration.
You can compute summary values for both expressions and columns. Any expression or column that appears in the compute clause must appear in the select list.
Aliases for column names are not allowed as arguments to the row aggregate in a compute clause, although you can use them in the select list, the order by clause, and the by clause of compute.
In a select statement with a compute clause, the order of columns in the select list overrides the order of the aggregates in the compute clause. Open Client™, JDBC, and DB-Library™ programmers must be aware of this in order to put the aggregate results in the right place.
You cannot use select into in the same statement as a compute clause, because statements that include compute do not generate normal tables.
The compute clause cannot contain more than 255 aggregates.
The group by clause cannot contain more than 255 columns.
Columns included in a compute clause cannot be longer than 255 bytes.