What do you mean by constraint ? What are the different type of constraint in MySQL? Explain

In the context of databases, a constraint is a rule that is applied to data columns in a table. It is used to limit the type of data that can be stored in a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted.

In MySQL, there are several types of constraints:

1. NOT NULL Constraint: This constraint ensures that a column cannot have a NULL value.

2. UNIQUE Constraint: The UNIQUE constraint ensures that all values in a column are different.

3. PRIMARY KEY Constraint: A PRIMARY KEY constraint uniquely identifies each record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.

4. FOREIGN KEY Constraint: A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table.

5. CHECK Constraint: The CHECK constraint is used to limit the value range that can be placed in a column. If you define a CHECK constraint on a single column it allows only certain values for this column.

6. DEFAULT Constraint: The DEFAULT constraint is used to provide a default value for a column. The default value will be added to all new records, if no other value is specified.

Each of these constraints serves a specific purpose and helps to maintain the integrity and accuracy of the data stored within your database.