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Code Lab is in development. New lessons and improvements are on the way. Progress can be deleted.
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Code Lab is in development. New lessons and improvements are on the way. Progress can be deleted.
SQL / POSTGRESQL / Learn / LESSON 03
NOT NULL forbids missing values. DEFAULT fills omitted columns. UNIQUE requires distinct values. CHECK limits valid values, e.g. pages > 0.
Small example:
CREATE TABLE books (
id INTEGER PRIMARY KEY,
title TEXT NOT NULL UNIQUE,
pages INTEGER NOT NULL DEFAULT 1 CHECK (pages > 0)
);The database starts empty. Grading checks the schema/data you create across variants.
Expected verify columns: column_name, column_name, is_nullable, has_default, constraint_type, id, title, pages · row order is checked
Expected final state (displayed data):
Loading…NOT NULL forbids missing values. DEFAULT fills omitted columns. UNIQUE requires distinct values. CHECK limits valid values, e.g. pages > 0.
QUERY STANDBY
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