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 working with complex joins, unions, and sub-queries.
- Complex joins - This competency includes using INNER, LEFT, RIGHT, and FULL joins on multiple tables and using joins for many-to-many relationships.
- Unions - This competency includes using unions to display multiple sets of information in the same report.
- Subqueries - This competency includes using data based on information returned from a different query. The ability to reduce selection set through the effective ordering of subqueries.