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Articles tagged with #databases
By the end of this page you can write a query that uses the answer to another query, recognise the four places one can go, spot the correlated kind that runs once per row, avoid the NOT IN that silent
By the end of this page you will have PostgreSQL running, a database of your own, and a working connection from a tool. You will also understand the shift that makes this feel harder than SQLite did:
If you want to write SQL against your own data today, install a file-based engine: SQLite if you are learning, DuckDB if your data is already in CSV files. Both give you the whole SQL language. Neithe
By the end of this page you can write a month-over-month growth query and trust its answer. You will know the growth formula and how to say it in a sentence, what LAG() actually does, and the three tr
By the end of this page you can predict what any query does when it meets a missing value, which is the skill that separates "my query returned nothing and I don't know why" from a two-second fix. You
By the end of this page you can check any table for duplicate rows, list every copy, and mark which one to keep, all with queries you understand. You will also know the step that comes before any quer
