PHP Variable Error When Selecting From Table - php

Question

I have a blog where I'm selecting the articles from a database using PHP. The problem is that becuase of my search terms I'm hitting an error. Here is my code:
<?php
if(isset($_GET["cat"])){
$cat = $_GET["cat"];
}else{
$cat = "all";
};
?>
<?php
if($cat == "all"){
$cat_var = "";
}else{
$cat_var = "WHERE cat = '$cat'";
}; // NOTE THIS LINE
?>
<?php
if(isset($_GET["issue"])){$issue = $_GET["issue"];}else{
$issue = "all";
};
?>
<?php
if($issue == "all"){
$issue_var = "";
$limit = 4;
}
else{
$issue_var = "AND issue = '$issue'"; // NOTE THIS LINE
$limit = 200;
};
?>
<?php
$count_posts_sql = "SELECT id FROM articles $cat_var $issue_var"; // NOTE THIS LINE
$count_posts_res = mysqli_query($con, $count_posts_sql);
$num_init_posts = mysqli_num_rows($count_posts_res);
//If None, Then Exit
if($num_init_posts == 0){
header("Location: /home");
exit();
}
...
?>
So my url would be http://website.com/articles/all/2015-10, which is what I want. However $cat_var & $issue_var is causing the error because it's selecting:
SELECT * FROM articles AND issue = '2015-10' // NO WHERE STATEMEMT IS SHOWN
How do I overcome this error?

Answer 1

You could get this going by sticking a WHERE 1=1 in
$count_posts_sql = "SELECT id FROM articles WHERE 1=1 $cat_var $issue_var"; // NOTE THIS LINE
This is because you start off with an AND value = 1 without starting the WHERE clause, which creates an invalid query.
Then take the WHERE out of this line and replacing it with an AND:
$cat_var = "AND cat = '$cat'";

Answer 2

You can initialize your where query string like this:
$where = 'WHERE 1 = 1 ';
and for there after you can concatenate depending on your inputs.