var str = "test";
console.log(str); // test
console.log(`str`) //str 这里的str是模板语法里面的，而不是变量str
console.log(`${str}`); //模板语法引入变量str, 输出 test
console.log(`‘${str}‘`); /输出 ‘test‘;
`INSERT INTO user (id, username, password) VALUES (0, ${req.body.username}, ${req.body.password})`
上面这样最后的结果是类似于 INSERT INTO user (id, username, password) VALUES (0, username, password) 这种结果
正确的做法应该是 INSERT INTO user (id, username, password) VALUES (0, ‘${req.body.username}’, ‘${req.body.password}’)
这样输出的才是 INSERT INTO user (id, username, password) VALUES (0, ‘username‘, ‘password‘)
