Databases Demystified a self teaching guide phần 6 ppt

... profile Composite Default screen 194 Databases Demystified Demystified / Databases Demystified / Oppel/ 225 364 -9 / Chapter 7 The Data Flow Diagram The data flow diagram (DFD) is the most data centric of all the ... privileges. 6. The update anomaly refers to a situation where: a. A simple update requires updates to multiple rows of data. b. Data cannot be updated because it do...

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

... 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 value for a ... one-to-many, one-to-one, or many-to-many 5. The Microsoft Access Show Table dialog box: a. Lists all tables in the database and allows for the metadata about tables to be added, changed, and...

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

... several proprietary XML databases on the market. However, businesses have been reluctant to abandon relational data - bases and undergo a major paradigm shift in the way they organize and store data. So, ... considered a best practice because it can lead to a lack of data sharing. Moreover, placing geographic or organizational unit names in table names plays havoc every time the organ...

Ngày tải lên: 08/08/2014, 18:22

... 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, followed by data marts: a. Will delay data mart ... screen CHAPTER 12 Databases for Online Analytical Processing 301 Demystified / Databases Demystified / Oppel/ 225 364 -9 / Chapter 12 Data Marts A data mart is a subset of...

Ngày tải lên: 08/08/2014, 18:22