Check if a row exists in another table using mysqli - php

Question

I am trying to select a row in one table and if it does exists in the second table,do something and if it doesn't,copy the values from table one into the second.
The problem is that,once it finds match (a row that is present in the first and second table),it shows errors for all other rows that did not match.
This is the error
Notice: Trying to get property of non-object in C:\wamp\www\loans.php on line 26
This is my code
<?php
//error_reporting(0);
$mysqli = new mysqli("localhost", "root", "123456", "test");
/* check connection */
if ($mysqli->connect_errno) {
printf("Connect failed: %s\n", $mysqli->connect_error);
exit();
}
$query = "select dest_msisdn,text_message,service_id,sender_name from incoming_sms";
if ($result = $mysqli->query($query)) {
/* fetch associative array */
while ($row = $result->fetch_assoc()) {
$dest_msisdn = $row['dest_msisdn'];
$text_message = $row['text_message'];
$service_id = $row['service_id'];
$sender_name = $row['sender_name'];
/**
Transactions
*/
$m = $mysqli->query("SELECT tel from transactions where tel = $dest_msisdn")->fetch_object()->message;
if(empty($m)){
$ti = "insert into transactions(message,tel) values($text_message,$dest_msisdn)";
$mysqli->query($ti);
}
}
/* free result set */
$result->free();
}
/* close connection */
$mysqli->close();
?>
I want to insert rows that i find in table one and are not in table two.

Answer 1

I suggest you check the rows yielded before accessing any properties that the result yields:
$m = $mysqli->query("SELECT tel, message from transactions where tel = $dest_msisdn");
// hi! im missing ^^
// you are accessing the property "message" but its not a selected column in your query
if($m->num_rows <= 0) {
$ti = "insert into transactions(message,tel) values($text_message,$dest_msisdn)";
$mysqli->query($ti);
}

Answer 2

When you chain like that you are assuming there will always be a row. When there isn't a row you cant get the property from it. That's why you get the error. So do something like this:
$r = $mysqli->query("SELECT tel from transactions where tel = $dest_msisdn");
if ($r->num_rows == 0) {
$ti = "insert into transactions(message,tel) values($text_message,$dest_msisdn)";
$mysqli->query($ti);
}

Answer 3

This doesn't answer your question directly, but it will fix your problem and probably solve some others.
The way you are going about inserting (where you first SELECT and then loop through the results in PHP, then SELECT from another table, then INSERT) seems unnecessarily complex. You can get rid of your PHP loop and just execute the INSERT in a single SQL statement without all the PHP overhead. Let your DB do the work for you.
All of this:
$query = "select dest_msisdn,text_message,service_id,sender_name from incoming_sms";
if ($result = $mysqli->query($query)) {
/* fetch associative array */
while ($row = $result->fetch_assoc()) {
$dest_msisdn = $row['dest_msisdn'];
$text_message = $row['text_message'];
$service_id = $row['service_id'];
$sender_name = $row['sender_name'];
/**
Transactions
*/
$m = $mysqli->query("SELECT tel from transactions where tel = $dest_msisdn")->fetch_object()->message;
if(empty($m)){
$ti = "insert into transactions(message,tel) values($text_message,$dest_msisdn)";
$mysqli->query($ti);
}
}
/* free result set */
$result->free();
Could be changed to just this:
$mysqli->query("INSERT INTO transactions(message,tel) SELECT text_message, tel FROM transactions INNER JOIN incoming_sms on transactions.tel = incoming_sms.dest_msisdn")