217 custom query

[LukasFehring]

Description

Motivation and Context

Changes

Type Of Changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

How has This Been Tested?

• Database provider:
• Python version:
• Operating System:

Does this Close/Impact Existing Issues?

• Issue #X

What is Missing?

Checklist

• [x] My change is based on the latest stage of the develop branch.
• [ ] My change required a change of the documentation, which has been done.
• [ ] I checked that the documentation can be build, visualizes everything as expected, and does not contain any warnings.
• [x] I have added/adapted tests to cover my changes.
• [x] The tests can be executed successfully.
• [x] The notebooks can be executed successfully.
• [x] The notebooks can be executed with mysql as provider.
• [x] I have added a description of the changes to CHANGELOG.rst.