As a data engineer, you’re not just moving data from point A to point B—you’re building the pipelines that help decision-makers ask bigger, better questions. Imagine this:

  • “How many users signed up last week?”

  • “Which warehouse shipped the most orders?”

  • “What’s the average transaction value in each region?”

These questions aren’t answered by peeking at a single record in a database. They need aggregate functions—SQL tools that summarize data so you can make it useful, efficient, and ready for analysis.

In this lesson, you’ll learn to use COUNT, AVG, SUM, MIN, MAX, and GROUP BY to engineer meaningful insights from raw, messy tables.

Count with confidence

Before fancy dashboards show results or reports are shared, someone must do the basic counting—and that person is usually you. As a data engineer, the COUNT() function is one of your most useful tools. You might use it to check if the right number of rows were loaded, see how many records a job produced, or find out how many missing values (NULLs) are in a column. It’s a simple but powerful way to ensure your data is complete and ready to use.

Syntax

The following is the syntax to use the COUNT() function:

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