Learn sql
Short lessons written around the screening tests employers use. Read one, then take the test.
SELECT, WHERE and ORDER BYReading a table: choosing columns, filtering rows and sorting, with the mistakes that return wrong rows silently.Lesson 1
Joins and GROUP BYCombining two tables and summarising rows: the two topics every SQL interview asks about.Lesson 2
Subqueries, IN, EXISTS and the NULL trapsHow to nest one query inside another, and why NULL silently empties results in comparisons, NOT IN and counts.Lesson 3
Primary keys, foreign keys and changing data safelyWhat keys and constraints guarantee, how INSERT, UPDATE and DELETE work, and the WHERE-clause habit that prevents wiping a table.Lesson 4
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