NodeJS MySQL NULL 值
在本文中,将学习处理NULL值并在 NULL值的基础上进行 Query。
句法:
IS NULL;
IS NOT NULL;
返回值:
- 'IS NULL' 返回包含一个或多个 NULL 值的列中的行。
- 'IS NOT NULL' 返回列中不包含任何 NULL 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 SQL 发布者表预览和示例数据如下所示。
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);
});
});
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:
示例 2:
索引.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: