The CHECK constraint is an important integrity constraint in a Database Management System (DBMS) that is used to restrict the values that can be stored in a table. It ensures that data entered into a database satisfies a specified condition or rule. A database may contain large amounts of information, and without appropriate restrictions, users may accidentally enter invalid, unreasonable, or inconsistent values. The CHECK constraint helps maintain data accuracy, consistency, and reliability by allowing only those values that satisfy a predefined condition. In a relational database, a table consists of rows and columns. Each column may have certain requirements regarding the type and range of data that it can contain. While a data type specifies the general form of data, such as INTEGER, VARCHAR, DATE, or DECIMAL, it does not always specify whether a particular value is logically acceptable. For example, an INTEGER column used for storing the age of employees may accept negative numbers even though a negative age is not meaningful. Similarly, a salary column may accept a value of zero or a negative amount unless an appropriate restriction is applied. The CHECK constraint can be used to prevent such invalid values. The basic syntax for defining a CHECK constraint is: ```sql CREATE TABLE table_name ( column1 datatype, column2 datatype CHECK (condition), column3 datatype ); ``` A CHECK constraint can be applied directly to an individual column or can be defined at the table level. A column-level CHECK constraint generally applies to the value entered in that particular column. For example: ```sql CREATE TABLE Employee ( Employee_ID INT, Name VARCHAR(50), Age INT CHECK (Age >= 18), Salary DECIMAL(10,2) CHECK (Salary > 0) ); ``` In this example, the Age column can contain only values that are 18 or greater, while the Salary column must contain a value greater than zero. If an attempt is made to insert an employee whose age is 15 or whose salary is negative, the DBMS will reject the operation because the