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; ​ ..