Progression

SQL · Intermediate - build real things

• INNER JOIN: connecting two tablesCross-reference data from two tables with INNER JOIN, readable aliases and a precise join condition.
• LEFT JOIN and NULL: finding what is missingKeep every row of a table with LEFT JOIN, spot absences with IS NULL and replace them with COALESCE.
• Subqueries: WHERE, FROM, IN and EXISTSNest one query inside another to compare against an aggregate, filter on a set or test for existence.
• Creating a schema: CREATE TABLE and constraintsDesign your own tables with suitable types and NOT NULL, UNIQUE and PRIMARY KEY constraints that protect your data.
• Foreign keys and referential integrityGuarantee consistency between your tables with REFERENCES and deliberately choose the ON DELETE behaviour.