using "INSERT INTO" statement in php code doesn't work - php

Question

I'm trying to build a database for a bookstore with 3 tables: Book, Volume and Publication. I'm using mysqli() and the code neither works nor echoes any errors.
<?php
//connect to db
$conn = new mysqli("localhost", "root", "", "ershadbookstore");
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
#new recoed: if the new record is inserted into book successfully, another new record is inserted into volume table. the same goes for volume and phblication table. at the end the total number of this volumn is editted in the rows with the same isbn.
$sql = "INSERT INTO Book (name, vnum, writer, translator, publisher, genre, format)
VALUES ('test', 'test', 'test', 'test', 'test', 'test', 'test')";
if ($conn->query($sql) === TRUE) {
$last_bid = $conn->insert_id;
$sql = "INSERT INTO Volume (isbn, bid, vnum, note, image)
VALUES ('test', 'test', 'test', 'test', 'test')";
if ($conn->query($sql) === TRUE) {
$sql = "INSERT INTO Publication (isbn, pubnum, pyear, circulation, fpyear, pnum, price, num)
VALUES ('test', 'test', 'test', 'test', 'test', 'test', 'test', 'test')";
if ($conn->query($sql) === TRUE) {
$sql= "SELECT SUM(num) FROM Publication
WHERE (isbn='test')";
if ($conn->query($sql) === TRUE) {
$totalNum=$conn->query($sql);
$sql1= "UPDATE Volume
SET (tnum = test)
WHERE (isbn= test)";
if ($conn->query($sql1) === TRUE)
{
echo "true";
}
else
{
return "Error publication table: " . $sql1 . "<br>" . $conn->error;
}
}
}
else{
return "Error publication table: " . $sql . "<br>" . $conn->error;
}
}
else {
return "Error for volume table: " . $sql . "<br>" . $conn->error;
}
}
else {
return "Error for book table: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>

Answer 1

The problem is that you are checking with === TRUE.
As PHP Manual says:
Returns FALSE on failure. For successful SELECT, SHOW, DESCRIBE or EXPLAIN queries mysqli_query() will return a mysqli_result object. For other successful queries mysqli_query() will return TRUE.
While your error checking would work for INSERT or UPDATE queries the SELECT query will not return true. In fact checking like this for boolean values is completely unnecessary.
Remove the check for === TRUE and your code should work fine.
$sql= "SELECT SUM(num) FROM Publication
WHERE isbn='test'";
if ($conn->query($sql)) { // removed === TRUE
$sql1= "UPDATE Volume
SET tnum = 'test'
WHERE isbn= 'test'";
if ($conn->query($sql1))
{
echo "true";
}
else
{
return "Error publication table: " . $sql1 . "<br>" . $conn->error;
}
}
If you enable mysqli error reporting, you don't need any if statements, which will make your code much simpler:
$sql = "SELECT SUM(num) FROM Publication
WHERE isbn='test'";
$conn->query($sql);
$sql1 = "UPDATE Volume
SET tnum = 'test'
WHERE isbn= 'test'";
$conn->query($sql1);
echo "true";
In addition, your values in the last update queries are missing quotes.
SET (tnum = 'test')
WHERE (isbn= 'test')";
Also there is no need to execute your SELECT query twice to get the values. You should refactor your code so that the second query ($totalNum=$conn->query($sql);) is not needed.

Answer 2

Also remove the triple equals === you are not comparing so you don not need a comparison operator so instead use !== FALSE
Example
if ($conn->query($sql) !== FALSE)
so this is saying if its not FALSE, than its TRUE so it will continue to run.