TIL_21.03.02(화)~03(수)

03.02(화)

SQL DATABASE w3shcool

CREATE DATABSE
Write the correct SQL statement to create a new database called testDB.

CREATE DATABASE testDB;

DROP DATABASE
Write the correct SQL statement to delete a database named testDB.

DROP DATABASE testDB;

CREATE TABLE
Write the correct SQL statement to create a new table called Persons.

CREATE TABLE Persons (
  PersonID int,
  LastName varchar(255),
  FirstName varchar(255),
  Address varchar(255),
  City varchar(255) 
);

DROP TABLE
Write the correct SQL statement to delete a table called Persons.

DROP TABLE Persons;

ALTER TABLE
기존 테이블에서 열을 추가, 삭제 또는 수정. 기존 테이블에 다양한 제약조건을 추가 및 삭제하는데도 사용.

ALTER TABLE table_name 
ADD column_name datatype;

or

ALTER TABLE table_name
DROP COLUMN column_name;

or

ALTER TABLE table_name
MODIFY COLUMN column_name datatype;

TRUNCATE TABLE
Use the TRUNCATE statement to delete all data inside a table.

TRUNCATE TABLE Persons;

Add a column of type DATE called Birthday.

ALTER TABLE Persons
ADD Birthday DATE
;

Delete the column Birthday from the Persons table.

ALTER TABLE Persons
DROP COLUMN Birthday;

SQL 제약

• NOT NULL
• UNIQUE
• PRIMARY KEY - not null과 unique의 조합. 테이블의 각 행을 고유하게 식별.
• FOREIGN HEY - 다른 테이블에서 행 / 레코드를 고유하게 식별
• DEFALUT

03.03(수)

sql 문제

프로그래머스 sql문제 뽀개기

새로알게 된 개념
w3school | HAVING 절
w3school | IFNULL
w3school | IF
w3school | Case
w3school | DATE_FORMAT()