Courses

Module 14: Writing the results and recommendations

A SQL result can be correct and still make a weak report. The table gives the numbers, but the reader still needs to know what they mean and what they…

Oct 4 • Cornellius Yudha Wijaya

Module 13: When a SQL query needs optimization

In this module, we will learn how to read a PostgreSQL query plan and decide whether an index is worth keeping.

Oct 4 • Cornellius Yudha Wijaya

Module 12: Checking whether your result is right

Let's learn how to check a SQL result before we use it in a report or recommendation.

Oct 2 • Cornellius Yudha Wijaya

Module 11: Using window functions without changing the row count

Let’s learn how to calculate totals, running values, and ranks while keeping every order row in the result.

Oct 2 • Cornellius Yudha Wijaya

Module 10: Breaking a query into steps with subqueries and CTEs

Let's learn how to split a long SQL query into named steps and check the result from each step.

Oct 2 • Cornellius Yudha Wijaya

Module 9: When a join increases your numbers

Let's learn why a one-to-many join can increase a total and how to keep the number correct.

Oct 1 • Cornellius Yudha Wijaya

Module 8: Choosing between INNER JOIN and LEFT JOIN

Let's learn how `INNER JOIN`, `LEFT JOIN`, and filter placement change the rows in our result.

Sep 30 • Cornellius Yudha Wijaya

Module 7: How to define a metric clearly

Let's learn how to define a conversion rate so another person can calculate the same number.

Sep 29 • Cornellius Yudha Wijaya

Module 6: WHERE and HAVING: filtering before and after GROUP BY

Let's learn when a condition belongs in `WHERE` and when it belongs in `HAVING`.

Sep 26 • Cornellius Yudha Wijaya

Module 5: Counting the right thing with GROUP BY

Let's learn how `GROUP BY` changes the result and why `COUNT(*)` doesn't always count the thing we need.

Sep 20 • Cornellius Yudha Wijaya

Module 4: Finding the top results with ORDER BY and LIMIT

Let's learn how `ORDER BY` and `LIMIT` choose the top or bottom rows, and what to do when several rows tie at the cutoff.

Sep 20 • Cornellius Yudha Wijaya

Module 3: Filtering data with WHERE and NULL values

Let’s see how NULL values and time zones change the rows we get from a WHERE clause.

Sep 20 • Cornellius Yudha Wijaya

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