Product records
Keep users, projects, orders, and activity connected and consistent.
Why SQL?
Ask better questions of data and make the answers reliable.
Where SQL earns its place.
Applications depend on records that must be stored, joined, updated, and retrieved correctly. SQL skills help you understand what the software is doing with data, diagnose slow requests, and make changes without damaging the information people rely on.
Reporting
Turn operational data into useful answers for a team or customer.
Performance work
Use indexes and query plans to improve slow data access.
Fix a report that is both slow and wrong.
A team asks for monthly order totals by customer. The first query joins orders to order items and repeats order amounts, so totals are inflated. As the data grows, the report also slows down.
The constraint
The answer must remain correct for customers with zero orders, multiple items, and cancelled orders.
Define the answer
Decide which orders count and what one row in the final report represents.
Write and inspect
Join and aggregate at the right level, then read the query plan on realistic sample data.
Improve and verify
Compare results before and after an index or rewrite; check both correctness and execution cost.
What you would produce
A correct report query, its query plan, and a short explanation of the change that made it faster.
Try an engineer’s decisionWould adding DISTINCT to the total fix a report inflated by an order-items join?
Usually not. DISTINCT can hide duplicate rows while also removing legitimate equal values. First define the grain of the result, then aggregate items or orders at that grain before joining.
This is an illustrative task. The scope of a module is agreed before enrolment.
What you would learn by doing it.
Each part of the exercise connects a tool or concept to a decision you would make on a software team.
Joins and aggregation
Choose keys and grouping based on the question the report answers.
You avoid totals that look plausible but are wrong.Query plans and indexes
Read how the database executes a query before adding an index.
Performance decisions are based on evidence from the data.Safe data changes
Use constraints and transactions where data must remain consistent.
A new feature does not quietly damage existing records.How real teams use SQL.
Published product and engineering sources show the kind of work this skill supports.
GitLab
GitLab documents PostgreSQL as the store for project, issue, merge request, and user metadata.
Read the source: GitLab architecture docsGitHub
GitHub has described MySQL databases behind repositories, users, issues, and pull requests.
Read the source: GitHub engineeringThese organizations are examples of technology in use. They are not affiliated with PixyDelta.
Find your starting point.
Work through a practical problem with a working engineer and review the decisions behind your result.
Safikul IslamFull-stack developer · In-person sessions