what do i need to use sql code example

Example: how do you use sql

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).