Node.js MySQL 空值

原文:https://www.geeksforgeeks.org/node-js-mysql-null-values/

在本文中，将学习处理空值并在空值的基础上进行查询。

语法:

IS NULL;

IS NOT NULL;

返回值:

• “为空”返回列中包含一个或多个空值的行。
• “不为空”返回列中不包含任何空值的行。

模块安装:使用以下命令安装 MySQL 模块。

npm install mysql

数据库:我们的带有样本数据的 SQL 发布者表预览如下所示。

例 1:

index.js

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 the query
    let query = "SELECT * FROM users WHERE address IS NULL";

    db_con.query(query, (err, rows) => {
        if(err) throw err;

        console.log(rows);
    });
});

输出:

例 2:

index.js

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 the query
    let query = "SELECT * FROM users WHERE address IS NOT NULL";

    db_con.query(query, (err, rows) => {
        if(err) throw err;

        console.log(rows);
    });
});

输出:

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