用于SQL搜索的IF语句

Question

I have an HTML page where a person can enter information to search through a database. The options are: Author, Title, Category, Year, and ISBN.

A person can enter an Author name to search for books written by them. However, I want them to be able to put Author name + Category to retrieve records. The code underline does not function properly.

Any help will be appreciated.

$Author = $_POST["Author"];
$Title = $_POST["Title"];
$Category = $_POST["Category"];
$Year = $_POST["Year"];
$ISBN = $_POST["ISBN"];

// VIEW RECORDS WITH FOR STATEMENT
// How to filter through 2 or more filter statments ? ? ?  Title = '$Title' , Category = '$Category', Year = '$Year', ISBN = $ISBN


if (isset($Author) AND is_null($Title) AND is_null($Category) AND is_null($Year) AND is_null($ISBN)) {
    $sql = "SELECT * FROM Test WHERE Author = '$Author'";
    echo $sql;
} elseif (isset($Author) AND isset($Title) AND is_null($Category) AND is_null($Year) AND is_null($ISBN)){
    $sql = "SELECT * FROM Test WHERE Author = '$Author' AND Title = '$Title'";
    echo $sql;
} elseif (isset($Author) AND isset($Title) AND isset($Category) AND is_null($Year) AND is_null($ISBN)){
    $sql = "SELECT * FROM Test WHERE Author = '$Author' AND Title = '$Title' AND Category = '$Category'";
    echo $sql;
} elseif (isset($Author) AND isset($Title) AND isset($Category) AND isset($Year) AND is_null($ISBN)){
    $sql = "SELECT * FROM Test WHERE Author = '$Author' AND Title = '$Title' AND Category = '$Category' AND Year= '$Year'";
    echo $sql;
} elseif (isset($Author) AND isset($Title) AND isset($Category) AND isset($Year) AND isset($ISBN)){
    $sql = "SELECT * FROM Test WHERE Author = '$Author' AND Title = '$Title' AND Category = '$Category' AND Year= '$Year' AND ISBN= '$ISBN'";
    echo $sql;
} else {
    echo "You did not enter anything!";
}

$result = mysqli_query($con, $sql);

echo "<table border=1>";
echo "<tr><th>Author</th><th>Title</th><th>Category</th><th>Year</th><th>ISBN</th></tr>";

while ($row = mysqli_fetch_assoc($result)) {
    echo "<tr><td>" . $row['Author'] . "</td><td>" . $row['Title'] . "</td><td>" .  $row['Category'] . "</td><td>" .  $row['Year'] . "</td><td>" .  $row['ISBN'] . "</td></tr>";
}
echo "</table><br><br>";

Answer 1

This looks like a little more appropriate solution.

<?php
$fields=array('Author','Title','Category','Year','ISBN');

$query="SELECT * FROM Test WHERE ";

$first=true;
//unset fields that were not provided. Could be done inside of the next foreach
//but for simplicity reasons we will just do it here
foreach($fields as $key=>$val)
{
        if(!isset($_POST[$val]))
                unset($fields[$key]);
}

//now we only have fields that have data
foreach($fields as $field)
{
        if($first)
        {
                $query.="`$field`='".$con->real_escape_string($_POST[$field])."' ";
                $first=false;
        }
        else
        {
                $query.=" AND `$field`='".$con->real_escape_string($_POST[$field])."'";
        }

}

$result = mysqli_query($con, $sql);

echo "<table border=1>";
echo "<tr><th>Author</th><th>Title</th><th>Category</th><th>Year</th><th>ISBN</th></tr>";

while ($row = mysqli_fetch_assoc($result))
{
        echo "<tr><td>" . $row['Author'] . "</td><td>" . $row['Title'] . "</td><td>" .  $row['Category'] . "</td><td>" .  $row['Year'] . "</td><td>" .  $row['ISBN'] . "</td></tr>";
}
echo "</table><br><br>";