Help with grouping results please

@Taffd and @phper -- two practical ways to make contiguous groups of three (with any leftover shown as the final smaller group): do it in SQL or do it in PHP. Important: grouping depends on row order, so always use an explicit ORDER BY for predictable results.

SQL (MySQL 8+ using window functions)

SELECT ((rn - 1) DIV 3) + 1 AS group_no, *
FROM (
  SELECT *, ROW_NUMBER() OVER (ORDER BY <order_col>) AS rn
  FROM my_table
) AS t
ORDER BY group_no, rn;

SQL (older MySQL using user variables)

SET @rn := 0;

SELECT ((rn - 1) DIV 3) + 1 AS group_no, *
FROM (
  SELECT @rn := @rn + 1 AS rn, t.*
  FROM my_table t
  ORDER BY <order_col>
) AS numbered;

Note: initialize the variable separately and number rows inside a subquery so the ORDER BY is applied before numbering. User-variable behavior can be non-deterministic in complex queries, so test results.

PHP (application-level grouping)

$rows = [];
$stmt = $pdo->query('SELECT * FROM my_table ORDER BY <order_col>');
while ($r = $stmt->fetch(PDO::FETCH_ASSOC)) $rows[] = $r;

$groups = array_chunk($rows, 3);
foreach ($groups as $i => $grp) {
  echo "Group ".($i+1)."\n";
  foreach ($grp as $row) echo $row['your_column']."\n";
}

Or stream and chunk on the fly to avoid storing everything in memory: increment a counter, push rows into a temporary array, output and reset when its size hits 3.

Performance notes: for typical sizes the DB solutions are efficient; PHP is simpler to control presentation. Index the column used in ORDER BY for faster sorting.