Give messy data a shape

Name the columns

SELECT * is a shrug. In a learning lab, name the columns you intend to show: title, language, completed.

FROM names the table. Everything after WHERE is the filter that keeps surprises visible.

SELECT title, language
FROM lessons
WHERE completed = 0;

Filter before you decorate

WHERE completed = 0 is a boolean stored as a number in many tables. Be explicit. Do not rely on a UI to hide finished work.

AND chains conditions. OR needs parentheses when the question gets compound.

Order is part of the answer

ORDER BY path keeps a catalog feeling like a magazine index instead of a hash dump.

Glossary

projection

The columns a SELECT keeps.

predicate

The test in a WHERE clause.

result set

The rows that survive the question.