One Pager Cheat Sheet

• SQL constraints provide an important way to maintain the reliability and accuracy of data in relational databases, by limiting the types of data that may be added, changed, or removed from tables.
• Applying SQL Constraints to tables helps us to enforce business logic, maintain relationship integrity, prevent bad data, improve performance, and ensure uniqueness.
• SQL Constraints are used to guarantee quality data, restrict allowed data, enforce business logic, maintain relationships, ensure uniqueness, and improve performance, helping to guarantee database rules are followed.
• A NOT NULL Constraint is utilized to ensure that a column that stores important data will never contain a blank value.
• The UNIQUE constraint ensures that the values in the column it is specified for are unique and cannot be repeated.
• A CHECK constraint can be used to enforce business rules and restrict data entry, by specifying that all records in a database column must adhere to a specified criterion.
• The DEFAULT constraint establishes a default value that will be used if no alternative value is provided for a record's designated column.
• A PRIMARY KEY is a unique identifier for a table's row which cannot be NULL, and it can be set either during the creation of the table or afterward with an ALTER statement.
• A FOREIGN KEY is a field in a table that uniquely identifies each row of another table, which is specified either when the table is created with a CREATE TABLE query or with an ALTER TABLE query.
• A primary key ensures data consistency and accuracy while establishing relationships between tables, so having more than one would be illogical.