如何找出列中具有最大數字的行？

Question

我有一個SQL查詢出外這 -

select * from (SELECT parent.item_name as name, parent.lft as lft 
FROM item_tree AS item, 
    item_tree AS parent 
WHERE item.lft > parent.lft AND item.rgt < parent.rgt 
    AND item.item_id = 6) 
     as ABC 

這將返回一個表 -

name | lft 

---

A  |  1 
B  |  2 
C  |  3 

但是，我需要C的值，因爲它有最大LFT值。 所以，我修改了代碼如下 -

select * from (SELECT parent.item_name as name, parent.lft as lft 
FROM item_tree AS item, 
    item_tree AS parent 
WHERE item.lft > parent.lft AND item.rgt < parent.rgt 
    AND item.item_id = 6) 
     as ABC 
    having ABC.lft = MAX(ABC.lft) 

現在，這個查詢無返回值。 這段代碼有什麼問題？

在此先感謝！

Answer 1

嘗試此查詢

SELECT name, lft 
    from (SELECT parent.item_name as name, parent.lft as lft 
    FROM item_tree AS item, 
     item_tree AS parent 
    WHERE item.lft > parent.lft AND item.rgt < parent.rgt 
     AND item.item_id = 6) 
      as ABC 
    ORDER BY lft DESC 
    LIMIT 1 

Answer 2

MAX是agregate函數，沒有GROUP BY就無法工作。

試試這個：

select * from (SELECT parent.item_name as name, parent.lft as lft 
FROM item_tree AS item, 
    item_tree AS parent 
WHERE item.lft > parent.lft AND item.rgt < parent.rgt 
    AND item.item_id = 6) 
     as ABC 
    order by ABC.lft desc limit 1