SQL

SQL is an industry-standard query language that works with relational databases. Unlike some earlier systems, queries are performed at the server and only the results are passed to a client. This resulted in the ability to work with large databases efficiently over a network.

This competency area includes understanding simple queries, relationships, and aggregators. 

Key competencies:

1. Simple Queries - This competency includes using SELECT, JOIN, GROUP BY, ORDER BY, WHERE, LIMIT
2. Relationships - This competency includes using JOIN in a one-to-many relationship scenario.
3. Aggregators - This competency includes using aggregations such as SUM, COUNT, AVG.