NodeJs MySQL 删除查询

我们使用 SQL DELETE Query 从 MySQL 表中删除具有某些条件的数据。

句法：

• 这将删除客户表的所有行，但其他所有内容将保持原样（索引等）。

  DELETE FROM users

• 这将删除用户表中 userId 为 2 的所有行。

  DELETE FROM users WHERE userId = 2

模块：

• mysql：处理sql连接和查询

  npm install mysql

SQL用户表预览：

示例 1：删除用户表中的所有行

Javascript

const mysql = require("mysql");
  
let db_con  = mysql.createConnection({
    host: "localhost",
    user: "root",
    password: '',
    database: 'gfg_db'
});
  
db_con.connect((err) => {
    if (err) {
      console.log("Database Connection Failed !!!", err);
      return;
    }
  
    console.log("We are connected to gfg_db database");
  
    // here is our query
    let query = 'DELETE FROM users';
  
    db_con.query(query, (err, rows) => {
        if(err) throw err;
  
        console.log('Cleared users Table');
    });
});

输出：

示例 2：删除 name = 'pratik' 的所有用户。

• 方法 1：硬编码值

Javascript

const mysql = require("mysql");
  
let db_con  = mysql.createConnection({
    host: "localhost",
    user: "root",
    password: '',
    database: 'gfg_db'
});
  
db_con.connect((err) => {
    if (err) {
      console.log("Database Connection Failed !!!", err);
      return;
    }
  
    console.log("We are connected to gfg_db database");
  
    // This is our Hard Coded Query
    let query = "DELETE FROM users WHERE name = 'pratik'";
  
    db_con.query(query, (err, rows) => {
        if(err) throw err;
  
        console.log('Number of rows deleted = ' + rows.affectedRows);
    });
});

• 方法二：动态查询

Javascript

const mysql = require("mysql");
  
let db_con  = mysql.createConnection({
    host: "localhost",
    user: "root",
    password: '',
    database: 'gfg_db'
});
  
db_con.connect((err) => {
    if (err) {
      console.log("Database Connection Failed !!!", err);
      return;
    }
  
    console.log("We are connected to gfg_db database");
  
    // notice the ? in below query
    let query = "DELETE FROM users WHERE name = ?";
      
    // Dynamic Value
    let name = 'pratik';
  
    // Notice the name variable below
    // It will replace the ? in query
    db_con.query(query, name, (err, rows) => {
        if(err) throw err;
  
        console.log('Number of rows deleted = ' + rows.affectedRows);
    });
});

输出：