Manual deletion of tables

or As
result, you see the number of rows for each client. When only the
client you want to delete has rows, you can truncate the tables
beforehand. This will significantly speed up the client deletion.

Copy & deletion of "unbalanced" tables

When
you identify tables, where only a few rows are contained in the clients
which will remain in the system and a huge amount of rows in the client
you want to delete, you can first copy all remaining rows in a new
table (assuming you want to delete client 100): After that, you just have to truncate the original table and insert all rows from the temp table: Rebuilding the primary index is a good thing to speed up the client deletion afterwards.

Automation of finding tables / preparing statements

If
there are many huge tables and the time windows is very small, you may
use a scripting language to prepare the SQL statements. I prefer Perl,
as I know this language and as Oracle comes with Perl and the DBI
module. Connecting to your database is pretty simple: You can start the script with $ORACLE_HOME/perl/bin/perl script.pl as oracle owner. Next
step will be to determine all client specific tables - in most cases,
the first column is named client, mandt or mandant. Here is a code
snippet which will give you number of rows in the remaining clients and
overall rows, you just have to adjust to your needs: