Define a primary key

Module C - Designing databases and entity-relationship diagramming. After studying this chapter you will be able to: Identify how databases and spreadsheets are both similar and different; list and describe the four steps in designing and building a relational database; define the concepts of entity class, instance, primary key, and foreign key; given a small operating environment, build an entity-relationship (E-R) diagram.

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It is normally a noun. An Entity would have one or many attributes. It may be physical object (e.g. person) event (e.g. appointment) concept (e.g. order). descriptor (describe properties of the entity, e.g. lastname of the person) ATTRIBUTE A property of an entity identifier (uniquely distinguish entity instances - primary key in relational context) composite (a group of attributes used as a single attribute) Describes the relationship between entities. Typically expressed in verbs (e.g. has). There are no well defined standards of the EER notation....

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The relationships between columns in different tables are typically described through the use of keys, which are implemented through referential integrity constraints and their supporting indexes. For example, in Figure 1-2, you can establish a link between the DEPTNO column in the second table, which is called a foreign key,to the DEPTNO column in the first table, which is referred to as the primary key of that table. Finally, even if you define many different indexes for a table, you don’t have to understand them or manage the data they contain.

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This is the most accessible architectural theory book that exists. Korydon Smith presents each common architectural subject—such as tectonics, use, and site—as though it were a conversation across history between theorists by providing you with the original text, a reflective text, and a philosophical text. He also introduces each chapter by highlighting key ideas and asking you a set of reflective questions so that you can hone your own theory, which is essential to both your success in the studio and your adaptability in the profession.

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Nine years has passed since the 1992 second edition of the encyclopedia was published. This completely revised third edition, which is a university and professional level compendium of chemistry, molecular biology, mathematics, and engineering, is refreshed with numerous articles about current research in these fields. For example, the new edition has an increased emphasis on information processing and biotechnology, reflecting the rapid growth of these areas.

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We show how a simple but innovative synthesis of key disciplines such as computing science and cognitive science, can be deployed in combination with such topics as ergonomics, e-learning, pedagogy, cognitive psychology, interactive system design, neuropsychology etc to create new learning worlds that boost human learning to meet the demands of the 21st century. 2.

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2,3 Xác định một khóa và các chỉ số chỉ số chính được sử dụng để cải thiện hiệu suất khi truy vấn dữ liệu, chẳng hạn như tìm kiếm trên các lĩnh vực và phân loại thông tin.

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[ Team LiB ] Recipe 6.9 Retrieving Constraints from a SQL Server Database Problem You need to programmatically define constraints in a DataSet and retrieve constraint information defined in a SQL Server database. Solution Use the INFORMATION_SCHEMA views and SQL Server system tables to get information about primary keys, foreign keys, and check constraints.

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