You can create a custom KPI by defining a valid SQL SELECT statement. You specify the SQL statement for a custom KPI in the Collector for user defined SQL.
To create a KPI through a SQL SELECT statement, follow the instructions described in the chapter (DI-1904) How to Create a KPI Through Defining a SQL SELECT Statement.
More information about this collector can be found in (DI-1904) Collector for user defined SQL.
Additionally, you can find an (DI-1904) Example: Number of Inactive Objects on the System