COALESCE(規格,‘ ‘)

或者

COALESCE(規格,0)

select *
from (
SELECT p2.name_template 產品, p3.pname 材料 ,p3.spec 尺寸,(select c2.name from product_part_info c1 LEFT JOIN res_huo c2 ON c1.hpartner_id=c2.id where p3.id=c1.product_tmpl_id order by c1.id limit 1) 客戶,(select khwl_code from product_custo_info where p3.id=
 
product_tmpl_id order by id limit 1) 物料號,p4.name 內部批次,p4.outsidename 外部批次,p1.庫存,p5.總庫存
FROM (SELECT SUM(qty) 存量,product_id,lot_id
FROM stock_kqty p1
WHERE location_id=${倉}
GROUP BY product_id,lot_id) p1
LEFT JOIN product_code p2 ON p2.id=p1.product_id
LEFT JOIN  product_tep p3 ON p3.id =p2.product_tmpl_id
 
LEFT JOIN stock_pci_lot p4 ON p4.id=p1.lot_id
LEFT JOIN (SELECT SUM(qty) 總存量,product_id
FROM stock_kqty p1
WHERE location_id=${倉}
GROUP BY product_id
) p5 ON p2.id=p5.product_id
) abc
where (產品 like‘%${產品}%‘ or COALESCE(材料,‘‘) like ‘%${產品}%‘ or COALESCE(尺寸,‘‘) like ‘%${產品}%‘ ) and (客戶 like ‘%${客戶}%‘
 
 or 客戶 is null ) and 庫存<>0
;

sql語句常用功能（null值轉換為0）