Node.js MySQL LEFT()函数
LEFT()函数是 MySQL 中的内置函数,用于获取给定字符串的特定大小的前缀。
句法:
LEFT(input_string, size_of_prefix)
参数: LEFT()函数接受上面提到的和下面描述的两个参数。
- input_string:我们将得到这个输入字符串的前缀
- size_of_prefix:前缀中的字符数
返回值: LEFT()函数返回一个字符串,它是特定大小的 input_string 的前缀。
模块:
- mysql:处理 MySQL 连接和查询
npm install mysql
SQL 发布者表预览:
示例 1:静态查询
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");
// here is the query
let query = "SELECT LEFT(name, 4) AS prefix_name FROM publishers";
db_con.query(query, (err, rows) => {
if (err) throw err;
console.log(rows);
});
});
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 = "SELECT LEFT(salary, ?) AS prefix_salary FROM publishers";
let sizeOfPrefix = 3;
// notice second argument in below function
db_con.query(query, sizeOfPrefix, (err, rows) => {
if (err) throw err;
console.log(rows);
});
});
输出:
示例 2: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 = "SELECT LEFT(salary, ?) AS prefix_salary FROM publishers";
let sizeOfPrefix = 3;
// notice second argument in below function
db_con.query(query, sizeOfPrefix, (err, rows) => {
if (err) throw err;
console.log(rows);
});
});
输出: