mychuyblog: July 2009

DATABASE

1. Table (database)
In relational databases and flat file databases, a table is a set of data elements (values) that is organized using a model of vertical columns (which are identified by their name) and horizontal rows. A table has a specified number of columns, but can have any number of rows. Each row is identified by the values appearing in a particular column subset which has been identified as a candidate key.
Table is another term for relations; although there is the difference in that a table is usually a multi-set (bag) of rows whereas a relation is a set and does not allow duplicates. Besides the actual data rows, tables generally have associated with them some meta-information, such as constraints on the table or on the values within particular columns.
The data in a table does not have to be physically stored in the database. Views are also relational tables, but their data are calculated at query time. Another example are nicknames, which represent a pointer to a table in another database.

Sample database tables

Species List - 205 rows
Local Name
ScientificName
SpeciesID
Abacate
Persea gratissima Gaertn.
1
Abiu
Ferdinandusa paraensis
2
abiu do sertão
Pouruma sp.
3
Abiurana
Pottery bilocularis (Winkler) Baehni
4
Açaí
Euterpe Oleraceae Mahrt.
5
Acapurana
Campsiandra laurifolia Benth.
6
Acerola
Malpighia glabra
7
Ajuru

8
Ameixa
Eugenia cuminii
9
Anani
Symphonia globulifera L.F.
10

2. Queries (database)

Queries are the primary mechanism for retrieving information from a database and consist of questions presented to the database in a predefined format. Many database management systems use the Structured Query Language (SQL) standard query format.

3. Forms (database)

Database Form
A database form is a window or screen of related fields from a database. It is used to enter data or browse and view data.
All forms contain a number of fields, each with a field-label . The field is a space to enter data. Forms layout the fields and field labels in a logical manner to make data entry user friendly.
In a database form the input is checked against the rules for the field-type and may be additional rules, such as not null. Forms may be also checked against field or table constraints defined in a database, such as foreign keys and table relationships.
OpenOffice.org Base can create database forms with the Form Wizard quickly.
Using and creating Database Forms
The following screencasts demonstrate how to create and edit database forms:
· Create a form using the form wizard.
· Edit a form.
· Delete a form.

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Wednesday, July 15, 2009

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