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2010年12月7日 #

SQL UNIQUE Constraint
摘要： SQL UNIQUE Constraint The UNIQUE constraint uniquely identifies each record in a database table. The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. Note that you 阅读全文
posted @ 2010-12-07 22:02 mr liao 阅读(295) 评论(0) 推荐(0) 编辑