The Library is currently in the process of being upgraded from Oracle Database Version 22.214.171.124 to 126.96.36.199.
Demos are being upgraded to reflect the new Container paradigm as well as EBR (Edition Based Redefinition) and may contain references to CDBs, PDBs,
and other objects you may not be familiar with such as CDB_OBJECTS_AE: Welcome to 12c.
Have you viewed the Library's main Table of Contents? If not ... [Click Here]
... scroll down the page and you will find links to the largest collection of Oracle Database demos on the net.
The WHERE Clause servers two different purposes. One is to limit the records affected by a DML statement. The second to join two or more tables, view, or materialized views for DML.
The following links all have demonstrations of using the WHERE clause ... each in a different context.