Select With a Filter
When selecting records from a table, you can filter the selection by using the "WHERE" statement:
Example
Select record(s) with the address "Park Lane 38":
let mysql = require('mysql');
let con = mysql.createConnection({
host: "localhost", user: "yourusername",
password: "yourpassword", database: "mydb"
});
con.connect(function(err) {
if (err) throw err;
con.query("SELECT * FROM customers WHERE address = 'Park Lane 38' ", function (err, result) {
if (err) throw err;
console.log(result);
});
});Save the code above in a file called "demo_db_where.js" and run the file:
Run "demo_db_where.js"
C:\Users\
Your Name
>node demo_db_where.jsWhich will give you this result
[ { id: 11, name: 'Ben', address: 'Park Lane 38'}
]Wildcard Characters
You can also select the records that starts, includes, or ends with a given letter or phrase.
Use the '%' wildcard to represent zero, one or multiple characters:
Example
Select records where the address starts with the letter 'S':
let mysql = require('mysql');
let con = mysql.createConnection({
host: "localhost", user: "yourusername",
password: "yourpassword", database: "mydb"
});
con.connect(function(err) {
if (err) throw err;
con.query("SELECT * FROM customers WHERE address LIKE 'S%' ", function (err, result) {
if (err) throw err;
console.log(result);
});
});Save the code above in a file called "demo_db_where_s.js" and run the file:
Run "demo_db_where_s.js"
C:\Users\
Your Name
>node demo_db_where_s.jsWhich will give you this result
[ { id: 8, name: 'Richard', address: 'Sky st 331'}, { id: 14, name: 'Viola', address: 'Sideway 1633'}
]Escaping Query Values
When query values are variables provided by the user, you should escape the values.
This is to prevent SQL injections, which is a common web hacking technique to destroy or misuse your database.
The MySQL module has methods to escape query values:
Example
Escape query values by using the mysql.escape() method:
let adr = 'Mountain 21';
let sql = 'SELECT * FROM customers WHERE address = ' + mysql.escape(adr);
con.query(sql, function (err, result) {
if (err) throw err;
console.log(result);
});You can also use a ? as a placeholder for the values you want to escape.
In this case, the variable is sent as the second parameter in the query() method:
Example
Escape query values by using the placeholder ? method:
let adr = 'Mountain 21';
let sql = 'SELECT * FROM customers WHERE address = ?';
con.query(sql, [adr] , function (err, result) {
if (err) throw err;
console.log(result);
});If you have multiple placeholders, the array contains multiple values, in that order:
Multiple placeholders
let name = 'Amy';
let adr = 'Mountain 21';
let sql = 'SELECT * FROM customers WHERE name = ? OR address = ?';
con.query(sql, [name, adr] , function (err, result) {
if (err) throw err;
console.log(result);
});