Taking three relations for example, applyin some relevant theories to discrete mathematics, this article converses the query of the universal quantifier problem into the query of equivalent existential quantifier, then to achieve it in SQL.

• 以三个关系为例，应用离散数学的有关理论，把具有全称量词的查询问题转换成等价的存在量词的直询问题，并用SQL语言予以实现，