如何查询带有条件的mysql上的左联接子选择？

Question

我正在准备一个HTML表，它将连接2个表。

我无法找出查询，该查询将显示条件为=“ issued and group by item。”的发出的数量的总和。

$results= mysqli_query($db,

"SELECT  r.id, 
 COALESCE(w.sum_requested_qty,0) as sum_requested_qty,
 w.sum_issued_qty,
 r.stock -COALESCE(w.sum_requested_qty,0) as available_inv FROM  rizal_inv r     
left join
(select item_id,  sum(IFNULL(requested_qty,0)) as sum_requested_qty ,
(SELECT SUM(IFNULL(requested_qty,0)) FROM wmr_items WHERE issuance_status ='issued'  ) as sum_issued_qty from  wmr_items group by item) w  on r.id = w.item_id  where r.stock > 0  ORDER BY ABS(r.id);
");

此代码不起作用：

(SELECT SUM(IFNULL(requested_qty,0)) FROM wmr_items 
WHERE issuance_status ='issued'  ) as sum_issued_qty from  wmr_items group by item)

它显示

  

mysqli_query（）：（21000/1242）：子查询返回多于1行