Last Updated: 28 May, 2023
MySQL constraints are a set of rules or conditions that define and enforce the integrity of data in a MySQL database. Constraints are used to ensure that the data in the database meets certain conditions, such as uniqueness, referential integrity, or data type requirements.
MySQL constraints can be applied at the column or table level. These rules are basically restrictions or limitations on data or records.
Constraints provide reliability, consistency, and accuracy of the data or records in the table.
MySQL provides the following types of constraints for different purposes:
PRIMARY KEY
A primary key constraint ensures that a column or set of columns in a table uniquely identifies each record in the table. It is a combination of NOT NULL and UNIQUE constraints.
A primary key constraint can be created using the PRIMARY KEY keyword when creating a table or by altering an existing table.
FOREIGN KEY
A foreign key is a column or group of columns in a database table that is used to link that table to another table. When a foreign key is defined in a table, it creates a relationship between the two tables.
In MySQL, we can create a foreign key constraint by using the FOREIGN KEY keyword in the table definition.
UNIQUE
A UNIQUE constraint can be added to a column or a group of columns in a table. It ensures that no two rows in the table have the same value for the specified column(s).
If we try to insert a row that violates a unique constraint, MySQL will throw a Duplicate entry error. Unique constraints help in maintaining data integrity and preventing duplicate data from being inserted into a table.
NOT NULL
The NOT NULL constraint ensures that a column in a table does not contain null values. The NOT NULL constraint can be specified when creating a new table or altering an existing table.
It is important to use the NOT NULL constraint appropriately in a database schema to ensure data consistency and prevent errors.
CHECK
A CHECK constraint is used to ensure that the data being inserted or updated in a column satisfies a specified condition.
DEFAULT
A DEFAULT constraint ensures that default values are inserted into the columns when no value is specified during an insert or update operation.
By using constraints, we can improve the quality and consistency of the data in our MySQL database. They also help prevent errors and inconsistencies that can arise when data is added, updated, or deleted in the database.
That's all, guys. I hope this MySQL article is helpful for you.
Happy Learning... 😀
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