2 same codes in PHP, one is wrong [duplicate] - php

Question

This question already has answers here:
When to use single quotes, double quotes, and backticks in MySQL
(13 answers)
Closed 4 years ago.
// Not working
$stmt = $connection->prepare( "INSERT INTO numbers (homePhone, mobilePhone, officePhone)".
" VALUES ($phone_1,$phone_2,$phone_3)");
$stmt->execute();
// Works
$stmt = $connection->prepare( "INSERT INTO numbers (homePhone, mobilePhone, officePhone)".
" VALUES (?,?,?)");
$stmt->execute([$phone_1, $phone_2, $phone_3]);
When the first one is executed, it prints the error:
Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 1
no such column: blablabla in
C:\Users\zahha\IdeaProjects\icd0007\index.php:78 Stack trace: #0
C:\Users\zahha\IdeaProjects\icd0007\index.php(78):
PDO->prepare('INSERT INTO peo...') #1 {main} thrown in
C:\Users\zahha\IdeaProjects\icd0007\index.php on line 78
The second one works perfectly. What is the problem? Just wondering.

Answer 1

You need quotes around the variables in the first one, to indicate that the values are string literals in SQL.
$stmt = $connection->prepare( "INSERT INTO numbers (homePhone, mobilePhone, officePhone)".
" VALUES ('$phone_1','$phone_2','$phone_3')");

Answer 2

To make the first one work, you should put the variables between '. For example:
$stmt = $connection->prepare( "INSERT INTO numbers (homePhone, mobilePhone, officePhone)".
" VALUES ('$phone_1','$phone_2','$phone_3')");
$stmt->execute();
Or taking them out of the string, like:
$stmt = $connection->prepare( "INSERT INTO numbers (homePhone, mobilePhone, officePhone)".
" VALUES ('".$phone_1."','".$phone_2."','".$phone_3."')");
$stmt->execute();