A catalog is automatically created when you create a schema. There is also a system-wide catalog that is always in the QSYS2 library.
When an SQL object is created in a schema, information is added to both the system catalog tables and the schema's catalog tables. When an SQL object is created in a library, only the QSYS2 catalog is updated. A table created with DECLARE GLOBAL TEMPORARY TABLE is not added to a catalog.
As the following examples show, you can display catalog information. You cannot INSERT, DELETE, or UPDATE catalog information. You must have SELECT privileges on the catalog views to run the following examples.