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Overview: A database must provide a mechanism that will ensure that all possible schedules are ·either conflict or view serializable, and ·are recover 阅读全文
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Transaction Concept: A transaction is a unit of program execution that accesses and possibly updates various data items. A transaction is the executio 阅读全文
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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 阅读全文
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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 阅读全文
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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 阅读全文
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Domain Types in SQL char(n). Fixed length character string, with user-specified length n. varchar(n). Variable length character strings, with user-spe 阅读全文
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Attribute Attribute values are (normally) required to be atomic; that is, indivisible The special value null is a member of every domain. Indicated th 阅读全文
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Mapping the entity relation model to the schema: Step 1. Mapping of Regular Entity Types• For each regular entity type create a relation that includes 阅读全文
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Relational Model: A relation is unordered set that contain the relationship of attributes that represent entities. A relational database consists of a 阅读全文
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Bubble Sort: Bubble sort is an algorithm to sort a list through repeated swaps of adjacent elements. It has a runtime of O(n^2). For nearly sorted lis 阅读全文