Correct way to add PHP variable in MySQL query?

I am very new to PHP and trying to select data from a MySQL field (in a ta开发者_开发知识库ble). I used the following query.

$token = $wpdb->query("SELECT ami_st_token_aut 
                         FROM $wpdb->users 
                        WHERE ID = '".$current_user->ID."' ");

The value in the ami_st_token_aut is a big number but when i echo $token, it is echoing out $current_user->ID instead of the big token number. What could be going wrong?

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Two ways of doing it.

If you're doing it with WordPress, use the wpdb->prepare function:

$token = $wpdb->get_var(
  $wpdb->prepare(
    "SELECT ami_st_token_aut FROM $wpdb->users WHERE ID=%d", $current_user->ID
  )
);

If you're doing it without Wordpress, use the mysql_real_escape_string function.

mysql_query(
  "SELECT ami_st_token_aut FROM tablename WHERE ID='" 
  . mysql_real_escape_string($ID) . "'"
);

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See the Wordpress Codex.

The $wpdb->query function returns the number of rows that matched your query (if you do a SELECT, anyway).

$wpdb->get_var is the function to use to get a single value from the database.