43693
Beschreibung
Mindmap von eleanorbradbury, aktualisiert more than 1 year ago
|
Erstellt von eleanorbradbury
vor mehr als 11 Jahre
|
|
Relational Database
Concepts
- data base terminology
- tables- contain data
about items, made of
rows and columns they
must have unique names
- records - single row
within a table, contains
data about a single
item or event
- fields - idividual items of
data in a record, also
know as attributes
- keys - primary key, single field that is
a unique ID for the record
- composite primiary key - where two or
more fields make up the primary key
- foreign key - primary key in another
table, field in another, used to join
the two together
- secondary key -
used to index a field
- tables- contain data
about items, made of
rows and columns they
must have unique names
- entities
- single objects or processes
- information about things
- each entity becomes a table
- entities linked by
relationships
- single objects or processes
- relationships
- links between
entities/tables
- one to one- where one record in a table is
linked to only one record in another table
- one to many - one record in a table is
linked to many records in a second
table
- many to many - the many link goes both
ways between two tables
- links between
entities/tables
- referential integrity
- ensuring that for every record in a table with a foreign key, there
is a record in the corresponding table with the primary key
- ensuring that for every record in a table with a foreign key, there
is a record in the corresponding table with the primary key
- normalisation
- process applied to data structures
- decreases redundancy
- increases integrity
- first normal form
- every data
value is atomic
- no repeating data
- primary key
- every data
value is atomic
- second normal form
- must be in 1NF
- non-key attributes
are dependant on the
entire primary key
- must be in 1NF
- third normal form
- in 2NF
- no functional dependancy between
non-key items
- in 2NF
- advantages of normalisation
- removes redundancy
- increases consistency
- increases integrity
- easier maintenance
- flexibility for future expansion
- removes redundancy
- disadvantages of
normalisation
- reduced database
performance
- problems with
hostorical
calculations
- reduced database
performance
- process applied to data structures
- data dictionary
- database about a database
- contains
design details
about the
database
- includes table name, field
name, data type, length,
validation, relationships,
security
- database about a database
- datatypes
- text/string - anything
not requiring a
calculation
- integer, whole numbers
only, not telephone
numbers
- real, numbers with decimal places
- boolean - one of two values
- date/time - store age
, dates, times
- look to see what the data will be used for
- text/string - anything
not requiring a
calculation
- parameters
- simple query
- query where there is only
one parameter
- query where there is only
one parameter
- complex query
- a query with more than one
parameter
- makes use of AND, OR and
NOT to join paramters
- a query with more than one
parameter
- static
- parameter is hard coded into the
query and cannot be changed by
the end user
- parameter is hard coded into the
query and cannot be changed by
the end user
- dynamic
- request for the parameter given to the
end user at run time usually by a
dialogue box
- request for the parameter given to the
end user at run time usually by a
dialogue box
- simple query
Möchten Sie kostenlos Ihre eigenen Mindmaps mit GoConqr erstellen? Mehr erfahren.