MySQL选择不重复并确定是否只有一个user_id

Question

I would like to run a query to show if there is one or more than one user_id for given poll_id.

Example 1: poll_id 1106 has only user_id 1 for all it's rows.

Example 2: poll_id 1106 has more than one user_id 1 for all it's rows.

Using the example given below, this php code works:

$sql = "
SELECT 1 
FROM xf_poll_vote
WHERE poll_id='1106'
having count(distinct user_id) > 1";

// execute SQL query and get result 
$sql_result = mysql_query($sql,$connection); 

// format results by row 
while ($row = mysql_fetch_array($sql_result)) { 

    $user_id[] = $row["user_id"];

}

$count = count($user_id);

echo $count;

Answer 1

Just a COUNT / DISTINCT I think.

SELECT poll_id, CASE WHEN COUNT(DISTINCT user_id) > 1 THEN 'Many' ELSE 'One' END AS ManyOrOne
FROM SomeTable
GROUP BY poll_id

Answer 2

select 1
from yourTable
where poll_id = @yourPoll_id
having count(distinct user_id) > 1

if returns you anything, that poll_id have more than one user. If not, only have one or zero users