Data warehouse
A data warehouse is a database built for analysis: it brings data from many systems into one place, keeps its history and organizes it for queries.
Select any words here to ask your Maestro about them.
Your store's database keeps each order's current status. On October 15 you count how many orders were waiting to ship at the end of each September day. What does the chart show?
What it's for: bringing the data from a business's systems (sales, payments, ads, accounting) into one place to analyze together, without slowing down the systems the business runs on. Examples: Snowflake, BigQuery, Amazon Redshift, and lakehouses like Databricks.
Vs. an app's database: an app's database holds how things are right now and changes every second. A warehouse keeps the history and is organized for big queries, often as a star schema.
How it's filled: by ETL jobs that copy the data every night or every hour, and models in SQL, often with dbt. Tools like Power BI query it.
Design one in the course Data Modeling for AI Agents.
How it's used
Where its data comes from
An online store's warehouse
- Online store: orders and their status todayEach system knows its own piece, and only as it is now.
- Payments: charges and refunds
- Ads: spend per day and campaign
- marked: Every night: copy all three into the warehouse, with a snapshot of the dayAn ETL or ELT job; the snapshots keep the history.
- Power BI and SQL read from the warehouse, not from the systemsSo a heavy report doesn't slow down the store.
When to look closer
Same day, two totals
October 14 revenue
- marked: Store: $8,412.30
The store and the warehouse disagree on yesterday's revenue, but no order is missing. What could it be?
Ask your Maestro about Data warehouse
It answers from the free course page closest to this word, the way it answers while you study.
You: What does "Data warehouse" mean, in plain words?
Your Maestro: I'll explain it with a case of yours: it sticks better than a definition. Which question about your business needs data from two systems at once?
Asking about: Answers from the page "What is exploratory data analysis, and what do I do first with a new table?"
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Related terms
- Database
A database stores data in connected tables, with rules for each column, so many people and programs can read and change it without stepping on each other.
- ETL (extract, transform, load)
ETL (extract, transform, load) copies data out of the systems where it's created, cleans and reshapes it, and loads it into a data warehouse so it can be analyzed together.
- Star schema
A star schema arranges data for analysis: a fact table of events, like sales, in the center, joined by keys to dimension tables (customer, product, date) that describe them.
- SQL
SQL is the language for asking a database for data: which columns, from which table, which rows and how to summarize them. You get a table back.