Channi Studies

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..

In this post, we will learn about CHECK constraint used 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 CHECK constraint is used to limit the values that can be used in a column.  Let's start from our employe..

In this post, we will take a look at two constraints in MySQL—UNIQUE and NOT NULL. UNIQUEUNIQUE constraint ensures that all values in a column are different. We can add a constraint to a table when we create it, or after.  Let's make a new table named product, that stores three columns: id, name, and price of the product. Say we don't want any duplicative product id's in the table. We can use UN..