SQL

SQL is the most underrated language on this list because most developers think they already know it. They do not. Basic SELECT/JOIN knowledge covers 20% of what SQL can do. Window functions, CTEs, lateral joins, and query plan analysis are skills that separate $90k data analysts from $160k senior data engineers. In 2026, SQL is gaining new relevance via DuckDB (analytical SQL on local files, used in AI data pipelines), BigQuery/Snowflake cloud data warehouses, and LLM-powered SQL generation that still requires human review. The argument for prioritizing SQL: it is the one language shared by developers, data scientists, and business analysts.