Channi Studies

You can think of FOREIGN KEY as a primary key from one table that can be found within a different table.FOREIGN KEY constraint is used to prevent actions that would destory links between tables.Using a FOREIGN KEY, we can establish a link between two tables.  Let's stary by creating a new table for customer data. We will have customer_id, first_name, and last_name columns, and customer_id will b..

AUTO_INCREMENT attribute can be applied to a column that is set as a key. Whenever we insert a new row, the primary key will be populated automatically.  Let's re-create the transactions table that we created before. DROP TABLE transactions; CREATE TABLE transactions( transaction_id INT PRIMARY KEY AUTO_INCREMENT, amount DECIMAL(5, 2)); We can verify AUTO_INCREMENT attribute applied in the..

Today I learned PRIMARY KEYS constraint in MySQL.Primary key constraint can be applied to a column where each value in that column must both be unique and not null.It's typically used as a unique identifier.   PRIMARY KEYS constraint가 유용할만한 예시를 하나 들어보겠습니다. 대한민국의 출생신고가 된 모든 사람들은 각기 다른 주민등록번호를 가지고 있습니다. 편의를 위해 우리가 대한민국의 모든 사람들의 이름과 주민번호 데이터베이스에 대한 접근 권한이 존재한다고 가정하겠습니다. 이 상황에서 만약에 대한민국에 거주중인 특정 인물 ..

Today I learned about DEFAULT constraint in MySQL!!!  W3Schools.comW3Schools offers free online tutorials, references and exercises in all the major languages of the web. Covering popular subjects like HTML, CSS, JavaScript, Python, SQL, Java, and many, many more.www.w3schools.com As you can guess from its name, DEFAULT constraint is used to set a default value for a colum. Let's start by checki..