The following constraints are commonly used in MySQL:

• Column Level
  • NOT NULL - Ensures that a column cannot have a NULL value
  • UNIQUE - Ensures that all values in a column are different
  • DEFAULT - Sets a default value for a column if no value is specified
  • PRIMARY KEY - A column or a set of columns that uniquely identifies each row in a table
• Table Level
  CHECK - Ensures that the values under a column satisfies a specific condition
• Database Level
  FOREIGN KEY - Ensures the values under a foreign key in a referencing match the values in the referenced table.

Click on Foreign Key Constraints for more details.

Click on Check Constraints for more details.