PHP mysqli是最简单的方法吗？

Question

The code snippet is meant to return the minimum and maximum id from each round in this table I'm just wondering if there is a less clunky way of doing this.

$query = "SELECT round FROM $tablename";
$rounds = Array();
if ($result = $Login->mysqli->query($query)) {
    while ($row = $result->fetch_array(MYSQL_ASSOC)) {
        $rounds[] = $row['round'];
    }
}
$rounds = array_unique($rounds);
$rounds = array_values($rounds);
$roundBound = Array();
foreach ($rounds as $roundNum) {
    $query = "SELECT MIN(id), MAX(id) FROM $tablename WHERE round = $roundNum;";
    $result = $Login->mysqli->query($query);
    $row = $result->fetch_row();
    $roundBound[] = $row[0];
    $roundBound[] = $row[1];
}

hurr...

Changed to,

$query = "SELECT MIN(id), MAX(id) FROM $tablename GROUP BY round";
    if($result = $Login->mysqli->query($query)) {
        while ($row = $result->fetch_row()) {
            $roundBound[] = $row[0];
            $roundBound[] = $row[1];
        }
    }

Answer 1

如何在单个查询中执行此操作：

SELECT MIN(id), MAX(id) FROM $tablename GROUP BY round

Answer 2

It'd be more efficient to run a single query and use a WHERE round IN (....) clause:

$round_clause = implode(',', $rounds);

$query = "SELECT round, MIN(id), MAX(id) FROM $tablename WHERE round IN ($round_clause) GROUP BY round";

As a general rule, doing a single query that returns a "large" number of rows is going to be more efficient than doing a series of smaller/single queries that only return few or one rows at a time. You only scan the indexes once, you only have to retrieve the data once.

Answer 3

use group by

using query in foreach is the worst practice I ever seen

SELECT Min(id), Max(id) FROM $tablename GROUP BY round