Node.js MySQL Count()函数
我们使用 MySQL 中的 COUNT()函数来计算满足 WHERE 子句的列中的行数。
句法:
COUNT([column_name])
参数: COUNT()函数接受单个参数,如上所述和如下所述。
- column_name:我们必须从中返回计数值的列的名称。
模块安装:使用以下命令安装mysql模块:
npm install mysql
数据库:我们的带有示例数据的 SQL发布者表预览如下所示:
示例 1:计算 id 大于 5 的发布者
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 COUNT(id) AS id_count FROM publishers WHERE id > 5";
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 COUNT(salary) AS salary_count FROM
publishers WHERE salary BETWEEN 5000 AND 10000";
db_con.query(query, (err, rows) => {
if(err) throw err;
console.log(rows);
});
});
使用以下命令运行index.js文件:
node index.js
输出:
示例 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 COUNT(salary) AS salary_count FROM
publishers WHERE salary BETWEEN 5000 AND 10000";
db_con.query(query, (err, rows) => {
if(err) throw err;
console.log(rows);
});
});
使用以下命令运行index.js文件:
node index.js
输出: