On the iSeries :
select table_name, number_rows from QSYS2.SYSTABLESTAT
where table_schema = 'PRODDTA'
order by number_rows desc
On SQL Server :
SELECT
t.NAME AS TableName,
s.Name AS SchemaName,
p.rows AS RowCounts,
SUM(a.total_pages) * 8/1024 AS TotalSpaceMB,
SUM(a.used_pages) * 8/1024 AS UsedSpaceMB,
(SUM(a.total_pages) - SUM(a.used_pages)) * 8/1024 AS UnusedSpaceMB
FROM
sys.tables t
INNER JOIN
sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN
sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
INNER JOIN
sys.allocation_units a ON p.partition_id = a.container_id
LEFT OUTER JOIN
sys.schemas s ON t.schema_id = s.schema_id
WHERE
t.NAME NOT LIKE 'dt%'
AND t.is_ms_shipped = 0
AND i.OBJECT_ID > 255
GROUP BY
t.Name, s.Name, p.Rows
ORDER BY
TotalSpaceMB desc, t.Name
On Oracle :
select owner, table_name, numrows from sys.alltables where owner = 'PRODDTA' order by numrows desc;