Constraints: What Are SQL Constraints

What Are SQL Constraints ? SQL constraints are rules applied to columns or tables in a relational database to limit the type of data that can be inserted, updated, or deleted. Limitations and constraints both serve to define the parameters within which entities operate, but their origins internal versus external highlight different challenges and strategies for mitigation or adaptation. Recognizing whether a restriction is a limitation or a constraint is crucial in identifying the most effective approach to addressing it, whether through internal improvements or by influencing or adapting to external conditions. Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table. The following constraints are commonly used in SQL: NOT NULL - Ensures that a column cannot have a NULL value UNIQUE - Ensures that all values in a column are different Domain Constraints In a database table, domain constraints are guidelines that specify the acceptable values for a certain property or field. These restrictions guarantee data consistency and aid in preventing the entry of inaccurate or inconsistent data into the database. The following are some instances of domain restrictions in a DBMS ? Data type constraints ? These limitations define the kinds of data that can be kept in a column. A column created as VARCHAR can take string values, but a ...