检查MySQL行是否存在- Node.JS

const mysql = require('mysql');

// 创建MySQL连接
const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: 'password',
  database: 'database_name'
});

// 连接到MySQL数据库
connection.connect();

// 检查MySQL行是否存在的函数
function checkRowExists(tableName, condition) {
  return new Promise((resolve, reject) => {
    const query = `SELECT COUNT(*) AS count FROM ${tableName} WHERE ${condition}`;
    connection.query(query, (error, results) => {
      if (error) {
        reject(error);
      } else {
        const count = results[0].count;
        resolve(count > 0);
      }
    });
  });
}

// 使用示例
checkRowExists('users', 'username = "john"')
  .then(exists => {
    if (exists) {
      console.log('行存在');
    } else {
      console.log('行不存在');
    }
  })
  .catch(error => {
    console.error('发生错误:', error);
  })
  .finally(() => {
    // 关闭MySQL连接
    connection.end();
  });