目录主键（Primary Key）创建主键超键（Super Key）创建超键候选键（Candidate Key）创建候选键外键（Foreign Key）创建外键实际应用结论在mysql数据库中，键（Key）是用于确保数据完整性和一致性的重要概念。键不仅
i have stored the txtfile in the database.i need to show the txtfile when i clik the link. and this link has to be created dynamically.
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