SQL and Databases: Ask Your Data Anything

By the end

What you'll build

• Explain why one table per kind of thing beats one wide sheet, and name the three anomalies it prevents
• Write SELECT queries with explicit column lists, computed columns and aliases
• Filter rows precisely with comparison operators, bracketed AND/OR/NOT, IN, BETWEEN and LIKE
• Find and handle missing data with IS NULL and COALESCE, and explain why = NULL silently returns nothing
• Sort and page results with ORDER BY, LIMIT and a unique tie-breaker so answers are repeatable
• Summarise data with COUNT, SUM, AVG, MIN and MAX, and choose correctly between COUNT(*) and COUNT(column)
• Group rows with GROUP BY, apply the rule about what may sit beside it, and filter groups with HAVING
• Join tables with INNER and LEFT JOIN, write an anti-join, join a table to itself, and spot an accidental cross join
• Restructure a nested query into a readable CTE and label rows with CASE WHEN
• Change data with INSERT, UPDATE and DELETE inside a transaction, writing the WHERE clause first
• Judge a table design against third normal form and decide when to denormalise on purpose
• Choose useful indexes and read a query plan well enough to tell a full scan from an indexed search

The shape of it

How this course works