Check if empty not working for me - php

Question

I want to check if a row value from my database is NULL or empty so I did the following:
$existcheck = "
SELECT *
FROM snm_content";
$existcheckcon = $conn->query($existcheck);
$existcheck = $existcheckcon->fetch_assoc();
if((!empty($existcheck['plaats'])) AND (!empty($existcheck['straat']))){
echo 'vol';
}else{
$vultable = "
ALTER TABLE snm_content
ADD (straat varchar(255) NULL,
plaats varchar(255) NULL)";
$vultablecon = $conn->query($vultable);
$vultable = $vultablecon->fetch_assoc();
$updatetable = "
UPDATE snm_content
SET straat = '".$straatnaam."', plaats = '".$bedrijven['plaats']."'";
$updatetablecon = $conn->query($updatetable);
$updatetable = $updatetablecon->fetch_assoc();
}
But I get the following message:
There was an error running the query [Duplicate column name 'straat']
Both straat and plaats in snm_content are all filled with NULL.
So why does it get to the else statement if the values are NULL?
I should mention, this code is inside a while loop from another query.

Answer 1

You should check if the column exist not if column have a data so you have to do like this :
$existcheck = "DESC snm_content";
$existcheckcon = $conn->query($existcheck);
$existcheck = $existcheckcon->fetch_assoc();
if((!empty($existcheck['plaats'])) AND (!empty($existcheck['straat']))){
echo 'vol';
}else{
$vultable = "
ALTER TABLE snm_content
ADD (straat varchar(255) NULL,
plaats varchar(255) NULL)";
$vultablecon = $conn->query($vultable);
$vultable = $vultablecon->fetch_assoc();
$updatetable = "
UPDATE snm_content
SET straat = '".$straatnaam."', plaats = '".$bedrijven['plaats']."'";
$updatetablecon = $conn->query($updatetable);
$updatetable = $updatetablecon->fetch_assoc();
}