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How to use SQL statements to perform data verification and integrity constraints in MySQL?
How to use SQL statements to perform data verification and integrity constraints in MySQL?
Dec 18, 2023 pm 07:03 PM
How to use SQL statements to perform data verification and integrity constraints in MySQL?
Data verification and integrity constraints are commonly used methods in database management systems to ensure the correctness and integrity of data. In MySQL, we can implement these constraints by using SQL statements. This article will introduce how to use SQL statements to perform data verification and integrity constraints in MySQL, and provide specific code examples.
1. Use CHECK constraints for data verification
CHECK constraints are used to verify the values ??of specific columns when inserting or updating data. The following is an example of using CHECK constraints:
CREATE TABLE Students (
student_id INT PRIMARY KEY,
student_name VARCHAR(50),
age INT,
CONSTRAINT check_age CHECK (age >= 18)
);In the above example, we created a table named Students, which contains three columns: student_id, student_name, and age. By adding a CHECK constraint on the age column, we ensure that the age value in all insert or update operations must be greater than or equal to 18.
2. Use UNIQUE constraints for unique constraints
UNIQUE constraints are used to ensure that each value in the column is unique. The following is an example of using UNIQUE constraints:
CREATE TABLE Employees (
employee_id INT PRIMARY KEY,
employee_name VARCHAR(50),
email VARCHAR(50) UNIQUE
);In the above example, we created a table named Employees, which contains three columns: employee_id, employee_name, and email. By adding a UNIQUE constraint on the email column, we ensure that the email value in the insert or update operation is unique.
3. Use FOREIGN KEY constraints for foreign key constraints
FOREIGN KEY constraints are used to ensure that foreign key columns in a table refer to primary key columns in another table. The following is an example of using FOREIGN KEY constraints:
CREATE TABLE Orders (
order_id INT PRIMARY KEY,
order_date DATE,
customer_id INT,
CONSTRAINT fk_customer_id FOREIGN KEY (customer_id) REFERENCES Customers(customer_id)
);In the above example, we created a table named Orders, which contains three columns: order_id, order_date and customer_id. By adding a FOREIGN KEY constraint on the customer_id column and referencing the customer_id column of the Customers table, we ensure that the customer_id value in the insert or update operation must be valid.
4. Use NOT NULL constraint for non-null constraints
NOT NULL constraint is used to ensure that the value in the column is not empty. The following is an example of using NOT NULL constraints:
CREATE TABLE Products (
product_id INT PRIMARY KEY,
product_name VARCHAR(50) NOT NULL,
price DECIMAL(10,2) NOT NULL
);In the above example, we created a table named Products, which contains three columns: product_id, product_name, and price. By adding NOT NULL constraints on the product_name and price columns, we ensure that the values ??of these two columns cannot be null during insert or update operations.
The above is a brief introduction to using SQL statements to perform data verification and integrity constraints in MySQL. By using these constraints, we can effectively ensure the correctness and integrity of the data in the database and prevent invalid or inconsistent data from entering the database. In actual applications, multiple constraints can be used in combination according to specific needs and business logic to achieve more comprehensive data verification and integrity protection.
The above is the detailed content of How to use SQL statements to perform data verification and integrity constraints in MySQL?. For more information, please follow other related articles on the PHP Chinese website!
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