Select With a Filter
When selecting records from a table, you can filter the selection by using the "WHERE" statement:
Example
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:
C:\Users\Your Name>node demo_db_where.js
Which 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
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:
C:\Users\Your Name>node demo_db_where_s.js
Which 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
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
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:
Example
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);
});
