Вы пропустили запятую после этого столбца:
`p`.`name`
Вместо этого рассмотрите этот запрос:
SELECT i.itemtype AS Item
, p.name
, SUM(CASE
WHEN itemtype = 2148 THEN i.count
ELSE 0
END) AS Count
, SUM(CASE
WHEN itemtype = 2152 THEN i.count
ELSE 0
END) * 100 AS Count1
, SUM(CASE
WHEN itemtype = 2160 THEN i.count
ELSE 0
END) * 10000 AS Count2
FROM player_items AS i
LEFT JOIN players AS p ON i.player_id = p.id
WHERE i.itemtype IN (2148, 2152, 2160)
GROUP BY i.itemtype ASC
LIMIT 0, 30
Чтобы суммировать эти три столбца вместе, вы можете:
SELECT t.itemType AS Item, t.Count, t.Count1, t.Count2
, SUM(t.Count1, t.Count2, t.Count3) AS Total
FROM
(
SELECT i.itemtype AS Item
, p.name
, SUM(CASE
WHEN itemtype = 2148 THEN i.count
ELSE 0
END) AS Count
, SUM(CASE
WHEN itemtype = 2152 THEN i.count
ELSE 0
END) * 100 AS Count1
, SUM(CASE
WHEN itemtype = 2160 THEN i.count
ELSE 0
END) * 10000 AS Count2
FROM player_items AS i
LEFT JOIN players AS p ON i.player_id = p.id
WHERE i.itemtype IN (2148, 2152, 2160)
GROUP BY i.itemtype ASC
LIMIT 0, 30
) AS t
Или вы можете добавить еще CASE
SELECT i.itemtype AS Item
, p.name
, SUM(CASE
WHEN itemtype = 2148 THEN i.count
ELSE 0
END) AS Count
, SUM(CASE
WHEN itemtype = 2152 THEN i.count
ELSE 0
END) * 100 AS Count1
, SUM(CASE
WHEN itemtype = 2160 THEN i.count
ELSE 0
END) * 10000 AS Count2
, SUM(CASE
WHEN itemtype = 2148 THEN i.count
WHEN itemtype = 2152 THEN (i.count * 100)
WHEN itemtype = 2160 THEN (i.count * 10000)
ELSE 0
END) AS Total
FROM player_items AS i
LEFT JOIN players AS p ON i.player_id = p.id
WHERE i.itemtype IN (2148, 2152, 2160)
GROUP BY i.itemtype ASC
LIMIT 0, 30
Операторы CASE избавляют вас от необходимости запускать три дополнительных оператора SELECT
для получения одинаковых результатов.