无法插入外键值

Question

I've made two tables to store user information, and the photo information they uploaded. Everything goes well, except when I try to insert userID to photos table, mysql just don't take it. The problem might comes from the foreign key things, but I don't know how to fix it.

CREATE TABLE IF NOT EXISTS users (
  userID smallint(7) NOT NULL auto_increment,
  email varchar(60) collate utf8_unicode_ci NOT NULL default '',
  PRIMARY KEY  (userID),
  UNIQUE KEY email (email)
) ENGINE=INNODB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


CREATE TABLE IF NOT EXISTS photos (
 photoID MEDIUMINT(7) NOT NULL AUTO_INCREMENT,
 userID SMALLINT(7),
 title       VARCHAR(150),
 brief    TEXT,
 PRIMARY KEY(photoID),
 INDEX (userID),
 FOREIGN KEY (userID)
 REFERENCES users(userID)
 ) ENGINE=INNODB; 

And the sql command I used to insert information to photos table

$sql = "INSERT INTO photos (userID ,title, brief)".
       "VALUES ('$uid', '$title','$bodytext')";

Even if the $uid is replaced by a static number like '2', which exists in user table(userID), it's still cannot be inserted.

I took some advices to add mysql_error function, however, it doesn't show anything...

$sql = "INSERT INTO photos (userID ,title, brief)".
       "VALUES ('2', '$title','$bodytext')";
$res = mysql_query($sql);

if ($res === FALSE) {
  die(mysql_error());
}

return mysql_query($sql);

Answer 1

Have you checked the exact error message? the MySQL functions return 'FALSE' if the query fails:

$sql = "INSERT ...";
$res = mysql_query($sql);
if ($res === FALSE) {
    die(mysql_error());
}

This will output the exact reason the query is failing. Until you do this, we can at most guess at what the problem is.

Most likely the error is due to the extra comma you have in your values field:

$sql = "INSERT INTO photos (`userID` ,title, brief, )".
                                                  ^---here

that causes a syntax error.

Answer 2

Two simple debugging tips:

<1> Inspect the real SQL code you are sending to the server. Add this line to your PHP code:

echo htmlspecialchars($sql);

... find the query in the browser and paste it in your MySQL client (HeidiSQL, PHPMyAdmin or whatever). Pay close attention to the possible error messages.

<2> Check error conditions in all functions:

$con = mysql_connect(...);
if( !$con ){
   die( htmlspecialchars(mysql_error());
}
...
$res = mysql_query(...);
if( !$res ){
   die( htmlspecialchars(mysql_error());
}

Answer 3

You can't insert value for foreign key like all others. Take example from my code:

  mysql_query("INSERT INTO 'bikemodel' VALUES('1', 'Cougar 125', '2009', 'Scooter CVT 1sp 150cc', 'Scooter', 'Road Bike', '150', foreign key=1)");