Month: January 2021

Part 2: NOT NULL & Unique Constraints in SQL

by

NOT NULL Constraints The NOT NULL constraint ensures that the column contains no null values. Columns without the NOT NULL constraint can contain null values by default. NOT NULL constraints must be defined at the column level. A NOT NULL constraint prohibits a column from containing nulls. The NULL keyword by itself does not actually … Read more

Categories SQL

Part 1: Constraints in SQL

by

Purpose: Use a constraint to define an integrity constraint—a rule that restricts the values in a database. The Oracle server uses constraints to prevent invalid data entry into tables. You can use constraints to do the following: • Enforce rules on the data in a table whenever a row is inserted, updated, or deleted from … Read more