A表数据 B表数据 现在要把B表 B_COSTS 的值update到A表 A_COSTS 字段SQL语法: update a set (a.a_costs) = (select b.b_costs from b where a.id = b.id and a.a_id = b.b_id) where exists (select 1 from b where a.id = b.id and a.a_id = b.b_id)结果: