06 2022 档案
摘要：Basic Concepts: Search Key - attribute to set of attributes used to look up records in a file. An index file consists of records (called index entries
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摘要：Overview: A database must provide a mechanism that will ensure that all possible schedules are ·either conflict or view serializable, and ·are recover
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摘要：Transaction Concept: A transaction is a unit of program execution that accesses and possibly updates various data items. A transaction is the executio
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摘要：First Normal Form： Domain is atomic if its elements are considered to be indivisible units A relational schema R is in first normal form if the domain
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摘要：Join Expressions: Natural Join： Natural join matches tuples with the same values for all common attributes, and retains only one copy of each common c
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摘要：Null Values： It is possible for tuples to have a null value, denoted by null, for some of their attributes. null signifies an unknown value or that a
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摘要：Domain Types in SQL char(n). Fixed length character string, with user-specified length n. varchar(n). Variable length character strings, with user-spe
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