经过虚拟表生成数量累计，数量累计为何重复显示，比如上行应为零，却把应在下行的提上来了

SELECT a.日期, a.材料编号, a.材料名称, a.期初数量, a.购入数量, (select sum(b.购入数量) from 材料进销存初查询 as b where b.材料编号=a.材料编号 and b.日期<=a.日期) AS 购入累计, a.领料数量, (select sum(b.领料数量) from 材料进销存初查询 as b where b.材料编号=a.材料编号 and b.日期<=a.日期) AS 领料累计
FROM 材料进销存初查询 AS a;
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