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MySql 外键约束 之CASCADE、SET NULL、RESTRICT、空等类型分析和_MySQL

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2016-06-01 13:11:48944browse

Mysql外键 

主表，从表【MySql】//http://my.oschina.net/cart/blog/277624空、RESTRICT、NO ACTION删除：从表记录不存在时，主表才可以删除。删除从表，主表不变更新：从表记录不存在时，主表才可以更新。更新从表，主表不变//http://my.oschina.net/cart/blog/277624CASCADE删除：删除主表时自动删除从表。删除从表，主表不变更新：更新主表时自动更新从表。更新从表，主表不变//http://my.oschina.net/cart/blog/277624SET NULL删除：删除主表时自动更新从表值为NULL。删除从表，主表不变更新：更新主表时自动更新从表值为NULL。更新从表，主表不变



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