A standard query is good when you have a fixed group of employees, e.g. employees in a single department.
What if you have a list of employees belonging to different groups - a custom query will be more suitable. The custom query may look complex but it is not. If you are familiar with spreadsheets, e.g. MS Excel, then you should be familiar with formulas such as Sum, Average etc.

A custom query is similar in concept because conditions are set as formulas. Each custom query created is made up of one or more conditions. Records need to satisfy the condition before they can be selected.

Example: 'Employee Name = Andrew Ang' or 'Basic Salary > 5000'

Shows the identity of the custom query. This is the primary key for the CustomQuery table.
Example: Confirmed Emp / PromotedEmp etc

Stores a description about the query.
Example: Basic Personal Details / Personal Employment Details etc

Shows if it is a distinct option, in a form of a checkbox.

Shows if the user wants the query to be grouped by a specific topic, in a form of a checkbox.

The table list contains the string of how the tables are joined for this query.

Shows the identity of the master query.