This example collects statistics on the system-derived PARTITION column for the row-partitioned orders table and writes them to a user-defined QCD called myqcd.
Even though you have specified a sampling percentage of 30 percent, the system ignores it and uses a value of 100 percent. See Collecting QCD Statistics on the PARTITION Column of a Table.
COLLECT STATISTICS FOR SAMPLE 30 PERCENT ON orders COLUMN PARTITION INTO myqcd;