MySQL在一个查询中选择具有唯一行的随机行

Question

Is it possible to select x random rows from a table, where one of the rows have to be a special row (thereby with a special field value) within one query?

Basically what I'm trying to create is a Guessing Game, where you have x amount of questions, with x amount of possible (checkbox selectable) answers!

This is how I select the answers currently... With 2 query's

$answers = 4; // This is the max amount of answers

// Just for testing the question_id is manually set

$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` != 1 ORDER BY RAND() LIMIT " . ($answers - 1) . "";
$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` = 1 LIMIT 1";

The "question_id" tells which question we are talking about, and the "correct" just tells if that field is the correct answer

So is it possible to select x random rows from a table, where one of the rows have to be "the correct one", within one query?

Answer 1

may be use UNION ?

$answers = 4;

$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` != 1 ORDER BY RAND() LIMIT " . ($answers - 1) . "";

$query .= " UNION ";

$query .= "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` = 1 LIMIT 1";

With one single query, you will be able to get the desired result

http://dev.mysql.com/doc/refman/5.0/en/union.html

Answer 2

$query = "SELECT * FROM answers WHERE ... whatever ... AND `question_id` IN (5, 9, 12, 16, 2)

So, you first find the number of rows and then put the correct answer's ID in to the WHERE IN statement. Because you know the one you want, you can just surround it with random IDs from the table and then render them in a random fashion.