INNER JOIN

Concepts covered: sqlInnerJoin

Syntax Example What INNER JOIN Excludes Writing Clean Joins Professional SQL requires clear, unambiguous code. Column qualification and table aliases make your joins readable and maintainable. Column Qualification When joining tables, both tables might have columns with the same name. SQL needs to know which table's column you mean. You specify this using table.column notation. The Problem This query is AMBIGUOUS if both tables have a "name" column: Error: Column "name" is ambiguous. SQL does not know which table's "name" column you want. The Solution Use table.column notation to be specific: Table Aliases Table aliases give tables short nicknames. This makes queries easier to read and write, especially when table names are long. In production codebases, over 95% of join queries use aliase

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This section is part of the Joins: Beginner lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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