SQL overview

SQL (Structured Query Language) is the standard declarative language for querying, manipulating, and defining data in relational database management systems (RDBMS). Core constructs include SELECT with joins, aggregations, and window functions; DML (INSERT, UPDATE, DELETE); DDL (CREATE TABLE, ALTER); and transaction control (BEGIN, COMMIT, ROLLBACK). Each RDBMS (PostgreSQL, MySQL, SQLite, SQL Server, BigQuery) extends standard SQL with proprietary syntax, functions, and optimization hints. Modern analytical SQL (via BigQuery, Snowflake, DuckDB) adds features like PIVOT, QUALIFY, and ARRAY/STRUCT types. SQL skills are essential across data science, backend engineering, data engineering, and business intelligence domains.