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update的基本语法是update 表 set 字段 = 值 where 字段 = xxx

现有物料表materials(y_name,y_quantity), 产品表a(p_name,p_quantity),要将产品a所用的物料汇总到materials上

如果做关联网上给的一种写法不适用mysql

select a.p_quantity + m.y_quantity + b.p_quantity from materials m,pro_a a,pro_b b where a.p_name = m.y_name and b.p_name = m.y_name ;

应该是这么写:

update materials m left join pro_a a on m.y_name = a.p_name set m.y_quantity = a.p_quantity + m.y_quantity ;

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