Technology LearningCheat Sheet
DATABASECHEAT SHEETS
SHEET 06
Counting, Grouping and Subqueries
M.R. Sterling
Database Intro · Sheet 06
Counting, Grouping and SubqueriesSQLite
GROUP BY drawn as buckets of real rows, then the five aggregate functions, COUNT(*) against COUNT(column), HAVING, and LEFT JOIN for the zero groups. Then every kind of subquery, and the NULL that empties NOT IN.
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What is on this sheet
GROUP BY as buckets
The five aggregates
COUNT(*), COUNT(column), COUNT(DISTINCT)
Keep the zero groups
HAVING and WHERE
Scalar and IN subqueries
NOT IN and the NULL trap
Correlated, EXISTS and derived tables
Common mistakes
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