Databases Demystified a self teaching guide phần 9 docx

... profile Composite Default screen CHAPTER 12 Databases for Online Analytical Processing 301 Demystified / Databases Demystified / Oppel/ 225364 -9 / Chapter 12 Data Marts A data mart is a subset of a data warehouse ... contains more data than a data warehouse. e. The project has a lower overall cost than a data warehouse project. 16. Building a data warehouse first, foll...

Ngày tải lên: 08/08/2014, 18:22

... complicated joins and calculations from the database users. For example, views can easily calculate ages based on birth dates, and they can summarize data in nearly any way imaginable. 220 Databases ... numeric digits and cannot be larger than 99 ,99 9 (five digits) or smaller than 99 ,99 9 (again, five digits). Also, because the scale is 0, it cannot have decimal digits (that is, it must...

Ngày tải lên: 08/08/2014, 18:22

... models, a brief his - tory of databases, and the rationale for focusing on the relational model. Properties of a Database A database is a collection of interrelated data items that are managed as a ... database can be defined as the file that contains the data items. Oracle Corporation defines their database as a collec - tion of physical files that are managed by an instance of...

Ngày tải lên: 08/08/2014, 18:22

... screen Constraints A constraint is a rule placed on a database object (typically a table or column) that restricts the allowable data values for that database object in some way. These are most important ... relational databases were built by both IBM and UC Berkeley. e. Nearly all the commercial relational databases are descendents of either System R or INGRES. 18. Currently avai...

Ngày tải lên: 08/08/2014, 18:22

... unmatched data to NULL, and because null values are not greater than 1/1/ 199 8 (and in fact are not greater than, less than, or equal to anything), the criteria as written in Example 3 -9 would eliminate ... row are called aggregate functions. The following table shows aggregate functions that are commonly used in relational databases: Function Name Description AVG Calculates the average...

Ngày tải lên: 08/08/2014, 18:22

... that ends every SQL statement. In Oracle, a transaction is automatically started for each database user session as soon as the user connects to the database. At any time, the database user can ... table’s data. The ALTER TABLE Statement The ALTER TABLE statement may be used to change many aspects of the definition of a database table. Again, there is a wide variation in implementation a...

Ngày tải lên: 08/08/2014, 18:22

... systems. Databases that store historical data used solely for analytical purposes are not as subject to insert, update, and de - lete anomalies. Chapter 12 contains more information on databases that ... normalization rules • Storing redundant data in tables • Storing summarized data in tables Note also that normalization is intended to remove anomalies from databases that are used for...

Ngày tải lên: 08/08/2014, 18:22

... profile Composite Default screen 194 Databases Demystified Demystified / Databases Demystified / Oppel/ 225364 -9 / Chapter 7 The Data Flow Diagram The data flow diagram (DFD) is the most data centric of all the ... profile Composite Default screen 196 Databases Demystified Demystified / Databases Demystified / Oppel/ 225364 -9 / Chapter 7 • Flows of data are shown using l...

Ngày tải lên: 08/08/2014, 18:22

... even to a different version of the same vendor’s database). Connecting Databases to Java Applications Java started as a proprietary programming language (originally named Oak) that was developed ... that binds the API to the particular database and platform, and a definition known as the ODBC data source contains the information necessary for a particular application to connect with...

Ngày tải lên: 08/08/2014, 18:22

... Control Language (DCL), 90 , 122–124 Data Definition Language (DDL), 90 , 118–122 data encryption, 256–257 data flow diagram, 194 – 196 data integrity, 214 Data Manipulation Language (DML), 90 , 114–118 tuning ... Autonomous e. Analog 82. Database locks: a. Are implemented in exactly the same way by all major database vendors b. Are controls placed by the DBMS to reserve data so updates...

Ngày tải lên: 08/08/2014, 18:22