mysql_fetch_array和mysql_query在来自两个不同表的调用中不返回任何内容

Question

I have two tables books and users. books has a column id and users has a column called book_id . users table is populated by info about users who bought books from the store including the column book_id which referees to the id from books table.

My questions is, I have been trying to do this but with no success.

$query = mysql_query("SELECT * FROM books, users WHERE books.id='$id' OR users.id='$id' ");
while($row = mysql_fetch_array($query)){
    $info .= $row[0] . " " . $row[1] . "<br/>";
}
echo $info; 

Table books has some data but users is empty and I am getting nothing as an output!!! What am I missing??

Additional attempts:

SELECT * FROM books, users WHERE books.id='$id' returns empty results

SELECT * FROM books WHERE books.id='$id' returns 5 rows

Answer 1

You're missing the correct JOIN .

Table books has some data but users is empty and I am getting nothing as an output

Since users table contains no records you need to use LEFT | RIGHT LEFT | RIGHT or FULL join to get the result set, depending on what you're trying to accomplish.

Therefore try to change your query to

SELECT * 
  FROM books b LEFT JOIN
       users u ON b.id=u.book_id
 WHERE ... 

Here is SQLFiddle