Fix: How to enter data to MySQL by using foreign key value?

 To enter data into a MySQL table that uses a foreign key, you need to ensure that the value you're using as the foreign key already exists in the referenced table. Here are the steps to enter data into a MySQL table using a foreign key value:

1. **Create Tables**:

   Ensure you have two tables – the main table and the referenced (related) table. The main table will contain the foreign key, and the related table will contain the primary key.

   For example:

   ```sql

   CREATE TABLE authors (

       author_id INT PRIMARY KEY,

       author_name VARCHAR(255)

   );

   CREATE TABLE books (

       book_id INT PRIMARY KEY,

       title VARCHAR(255),

       author_id INT,

       FOREIGN KEY (author_id) REFERENCES authors(author_id)

   );

   ```

2. **Insert Data into the Referenced Table**:

   First, insert data into the table that is referenced by the foreign key. In the above example, you would insert authors into the `authors` table.

   ```sql

   INSERT INTO authors (author_id, author_name) VALUES (1, 'John Smith');

   ```

3. **Insert Data into the Main Table**:

   When inserting data into the table that contains the foreign key (in this case, the `books` table), make sure to use an existing author_id from the `authors` table.

   ```sql

   INSERT INTO books (book_id, title, author_id) VALUES (1, 'Example Book', 1);

   ```

   Here, we're referencing the author_id (1) that we inserted in the `authors` table.

By following these steps, you ensure that the foreign key in the `books` table references an existing author in the `authors` table. This maintains referential integrity and helps prevent data inconsistencies.

If you attempt to insert a value in the foreign key column that does not exist in the referenced table, MySQL will produce a foreign key constraint violation error.