The unique constraint ensures that no two rows have the same values in their columns. Check constraints are used to make certain that a statement about the data is true for all rows in a table. The main types of constraints in SQL are check, unique, not null, and primary constraints. The key factors in data integrity are constraints, referential integrity and the delete and update options. When using SQL, data validation is the aspect of a database that keeps data consistent. By practicing simple data validation rules, databases are more consistent, functional, and provide more value to their users. Since information is constantly being updated, deleted, queried, or moved around, having valid data is a must. Data validation is often a topic of great importance when it comes to databases.
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