This query returns list of tables in a database with their number of rows.
Query
select tabschema concat '.' concat tabname as table_name,
    card as rows, 
    stats_time
from syscat.tables
order by card desc
Columns
- table_name - table name with schema name
- rows - number of rows in table (cardinality) ; -1 if statistics are not collected.
- stats_time - date and time the statistics were last updated
Rows
- One row represents one table
- Scope of rows: all tables in a database including tables without rows
- Ordered by number of rows descending, from largest to smallest (in terms of number of rows)
Notes
Number of rows may be not up to date as it's taken from DB2 statistics. Statistics must be updated after tables has had many updates, or after reorganizing any of the tables. You can do it with RUNSTATS command.
You can see when they were last updated for particular table in stats_time column of this query.
Sample results

 
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                     
                                                                 
                                                             
                                                             
                                                             
                                                             
                                                                 
                                                             
                                                             
                                                                 
                                                             
                                                             
                                                             
                                                             Marcin Nagly
                                                                        Marcin Nagly
                                 IBM Db2
                                                                IBM Db2
                                 SQL Server
                                                                                                SQL Server
                                             Azure SQL Database
                                                                                                Azure SQL Database
                                             Oracle database
                                                                                                Oracle database
                                             Snowflake
                                                                                                Snowflake
                                             Amazon Redshift
                                                                                                Amazon Redshift
                                             Teradata
                                                                                                Teradata
                                             Vertica
                                                                                                Vertica
                                             PostgreSQL
                                                                                                PostgreSQL
                                             MySQL
                                                                                                MySQL
                                             MariaDB
                                                                                                MariaDB