SQL filtering and projection

Picking which rows and columns you want back with SELECT and WHERE.

Also known as: SELECT statements, WHERE clauses, basic SQL.

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Relational model: Data as tables of rows and columns, with no other structure implied.

SQL joins: Combining rows from two or more tables based on a matching column.
SQL aggregation and grouping: Collapsing many rows into one summary number per group, like a total or average per category.
Stored procedures and triggers: Code that lives inside the database itself: called on demand (procedure) or fired automatically on an event (trigger).
Database security and access control: Who's allowed to see or change what, enforced through roles, privileges, and protection against attacks like SQL injection.