IT 공부한거 올리는 블로그

Referential Actions ON DELETE CASCADE ON DELETE NO ACTION ON DELETE RESTRICT ON DELETE SET NULL ON DELETE DEFAULT ON DELETE CASCADE ON DELETE SET NULL Referential Actions은 referencing하는 테이블에서 건다 CREATE TABLE employee( empno int NOT NULL, empname varchar(45), title varchar(45) DEFAULT '사원', manager int, salary int, dno int, CONSTRAINT UQ_empname UNIQUE (empname), CONSTRAINT CH_salary CHECK (salar..

QUIZ Query 1: HOW many languages are spoken in the USA? SELECT CountryCode, COUNT(Language) FROM countrylanguage WHERE CountryCode='USA'; ​ Query2: Count how many languages are in the world SELECT COUNT(DISTINCT Language) AS languages FROM countrylanguage; INTERMEDIATE DDL MySQL constraints UNIQUE CHECK DEFAULT ​ DEFAULT는 title VARCHAR(45) DEFAULT '사원' UNIQUE는 CONSTRAINT UP_empname UNIQUE(empnam..

Data Definition Language DDL: 데이터베이스 구조를 다루는 언어 Statements CREATE //생성 DROP //삭제 ALTER //변경 TRUNCATE //데이터만 삭제 Database SQL CREATE DATABASE testDB; DROP DATABASE testDB; SHOW DATABASES; USE testDB; Relation SQL CREATE TABLE department( deptno INT NOT NULL, deptname VARCHAR(45) NOT NULL, floor INT CONSTRAINT PK_Deptno PRIMARY KEY(deptno) ); ​ DROP TABLE department; ​ TRUNCATE TABLE department; ​ ..

Data: 컴퓨터에서 보낼 수 있고 저장돼있는 파일들 ​ Database: an organized collection of data 구조를 가진 데이터의 모임 ​ ​ Data Model: 데이터를 저장, 연결, 접근하는 방식을 설명하는 것 ex) Realtional Model, Object-Oriented Model ... ​ ​ relation==table ​ DBMS(Database Manament System) : A software designed to store, retrieve, define, and manage data in a database 데이터베이스의 데이터를 다루는 소프트웨어 ex) Oracle, MySQL, MongoDB ... ​ ​ Query: 질의 dbms에서 어떤 정보를 요..