I've 20 tables in the database. How can I find the top table in volume?

Run the RUNSTATS utility and then check the column NPAGES of the
SYSIBM.SYSTABLES catalog table.
This columns stores the number of pages used by the table

Thanks, it's giving the pages information.

I've seen the rows in the SYSIBM.SYSTABLES and found that some values of NPAGES are -1.

Can any one please explain NPAGES=-1?

Did you RUNSTATS on the table?

-1 can also mean that the 'table' is a view or alias.

BTW, to know the size of the table, you'll have to multiply the npages with the pagesize of the tablespace.

Oh, don't forget the size of indexes either.

If you are using DB2 LUW, I would recommend using the catalog view SYSCAT.TABLES instead of the SYSIBM.SYSTABLES.

HTH

Sathyaram