My SQL 공부1(SLEECT, FROM, WHERE)

MYSQL 명령어 공부

많이 쓰이는 명령어

SELECT - extracts data from a database
UPDATE - updates data in a database
DELETE - deletes data from a database
INSERT INTO - inserts new data into a database
CREATE DATABASE - creates a new database
ALTER DATABASE - modifies a database
CREATE TABLE - creates a new table
ALTER TABLE - modifies a table
DROP TABLE - deletes a table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index

SELECT

table 에서 전체 데이터 선택하기

SELECT * FROM Customer

여러 데이터 선택하기

SELECT city, customer FROM Customer

중복되는 데이터는 없에기

SELECT DISTINCT Country FROM Customer

중복되는 데이터를 없엔 후 몇개인지 세어보기

SELCET COUNT (DISTINCT city) FROM Customer

 

WHERE

The WHERE clause is used to filter records(조건문)

 

city==mexico인 tuple  가져오기(String type)

SELECET country FROM Customer WHERE country='Mexico';

AND, OR, NOT

country: Germany, City: Berlin 인 tuple 가져오기,

SELECT * FROM Customers WHERE city='Berlin' and country='Germany'

country <>Germany 인것 가져오기

SELECT * FROM Customer WHERE NOT Country ='Germany'

 country = Germany 중에서 Berlin 과 Munchen city 가져오기

SELECT * FROM Customer WHERE Country='Germany' AND (City='Berlin'and City='Munchen');