Table and it's operations


Table and it's operations


Table/Entity

To represent this information one can use DBMS modeling. In a DBMS a group of similar information or data which is of interest to an organization is called an Entity. Entity information is stored in an object called Table. For example, a client is considered an entity. Information about the client entity can be stored in a client_master table. A table is really a two dimensional matrix that consists of rows and columns.

Attributes/Columns/Fields




Each entity can have a number of characteristics. A client can have characteristics like name, address, telephone number, fax number, balance due etc. The characteristics of an entity are called Attributes. The values for these characteristics are called Attribute Values.
When entity information is stored in a table, the attributes associates with the entity are stored in the table columns / table fields. The client_master table can have columns like name, address, telephone_number, fax_number, bal due in with the user can store attributes values like "Datamatics", "Vindhya Valley", "614572", "6122897", "2200.00".
Thus information in the client_master table will be

Name
Address
Telephone
Number
Fax Number
Balance 
Due
Datamatics
Vindhya Valley
614572
6122897
2200.00
THE DATA TYPES THAT A CELL CAN HOLD

Data Type
Description
CHAR(size)
:
This data type is used to store character string values of fixed length. The size in brackets determines the number of characters(i.e. the size) this data type can hold is 255 characters.
VARCHAR(size) / VARCHAR2(size)
:
The data type used to store variable length alphanumeric data. The maximum this data type can hold is 2000 characters.
NUMBER(P, S)
:
The NUMBER data type is used to store numbers (fixed or floating point). Numbers of virtually any magnitude maybe stored up to 38 digits of precision. Number as large as 9.99*10 to the power of 124, i.e. I followed by 125 zeros can be stored.
DATE
:
This data type is used to represent date and time. The standard format is DD-MM-YY as in 20-MAY-99.
LONG
:
This data type is used to store variable length character strings containing up to 2GB. LONG data can be used to store arrays of binary data in ASCII format. LONG values cannot be indexed, and the normal character functions such as SUBSTR cannot be applied to LONG values.
RAW/ LONG RAW
:
The RAW /LONG RAW data types is used to store binary data, such as digitized picture or image. Data loaded into columns of these data types are stored without any further conversion. RAW data type can contain up to 2GB. Values stored in columns having LONG RAW data type cannot be indexed.

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