Our web application uses Oracle database and 
I normally write queries to do Data validation. 
For example: 
I create data from UI or I send POST request
from API then I write query to verify that data
was successfully and correctly inserted into database.
Our database consists of many tables, so most of the time,
I need to write queries that involve joins.

CAN MENTION: Since our application has large sets of
data, data is stored into Oracle and to another CACHE database.
I write queries to test data that both are in SYNC(same).