MySQL选择多条件

Question

As beginner I have been struggling to find a solution to the following situation:

I have 3 tables:

Table 1: CITIES 
id|city
1|London
2|Paris


Table 2: CATEGORIES 
id|category
1|category1
2|category2

Table 3: PRODUCTS 
id|city|category|name|keyword
1|1|1|product1|keyword1
2|1|1|product2|keyword2

Now I need help to mysql select to display for search results, something like this:

<?php
$keyword = preg_replace('#[^a-zA-Z]#', '', $_GET['keyword']);
$city = preg_replace('#[^0-9]#', '', $_GET['city']);
$category = preg_replace('#[^0-9]#', '', $_GET['category']);

$result = mysqli_query($con,"SELECT * FROM products WHERE category = '$category' AND city = '$city' AND keyword LIKE '$keyword'");
while($row = mysqli_fetch_array($result)) {
$id = $row['id'];
$name = $row['name'];
$category = $row['category'];
$city = $row['city'];
}
?>

my url is: search.php?keyword=keyword&category=1&city=1 this is working fine but if any of arguments is missing, then is displaying 0 results

sample: search.php?keyword=&category=&city=1

Answer 1

you need dynamic sql generation check example below:

$query = "SELECT * FROM products WHERE 1=1"; // note default case, always true
if ($category)
    $query .= " AND category = ".intval($category, 10); // note intval
if ($city)
    $query .= " AND city = ".intval($city, 10);
if ($keyword)
    $query .= " AND keyword LIKE '%" . mysqli_real_escape_string($keyword). "%'"; // note escaping
$result = mysqli_query($con, $query);

UPDATE: you can use the same approach for queries with JOINS, check this out:

$query = "SELECT *
    FROM PRODUCTS
    inner join
    CATEGORIES on (PRODUCTS.category = CATEGORIES.id)
    inner join
    CITIES on (PRODUCTS.city = CITIES.id)
    WHERE 1=1";