https://blog.gongquiz.com/2021/10/01/%eb%8b%a4%ec%9d%8c-sql%eb%ac%b8%ec%9d%84-%ec%8b%a4%ed%96%89%ed%95%9c-%ea%b2%b0%ea%b3%bc%eb%8a%94-%eb%a9%80%ed%8b%b0%eb%af%b8%eb%94%94%ec%96%b4%ec%bd%98%ed%85%90%ec%b8%a0%ec%a0%9c%ec%9e%91%ec%a0%84/