Databases
Introduction - concepts
Concepts of Relational Databases
Domain definitions
Example
Catch Up
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Relation
table
file
Attribute
column
field
Tuple
row record
Domain
Cardinality
Candidate key primary key
foreign key
• Null
• Entity integrity (row have a primary key)
• Referential integrity ()
Entity Integrity
• Normal forms
– 1,2,3 NF
– Boyce-codd
– 4,5 NF
1st Normal Form
• The first normal form (1NF) is all about
eliminating repeating groups of data
• Guaranteeing atomicity (the data is selfcontained and independent). At a high level, it
works by creating a primary key
• In short: primary key + no double values
2nd Normal Form
• The table must be in 1NF
• Each column must depend on the whole key
i.e. only relevant for combined keys
part of columns can not be dependent of only
a part of the key
• In short: 1NF + all values(attributes) are
pointed out by the whole key
3rd Normal Form
• The table must be in 2NF
• No column can have any dependency on any
other non-key column
• You cannot have derived data
• In short: 2NF + all values(attributes) can
only be pointed out by the whole key
Referential Integrity
• Constraints on foreign key’s
– On Delete
– No Action, Null(0-*), Default, Cascade(composite / 1-*)
– On Update
– No Action, Null, Default, Cascade
– See more:
http://technet.microsoft.com/en-us/library/aa902684(v=sql.80).aspx
Structured Query Language
• Data Definition Language (DDL)
or data description language
– Define tables, relations, triggers, stored procedures, user datatype etc.
• Data Manipulation Language (DML)
– Request data (select)
– Update data (insert, update, delete)
Select (Read)
• Select (columns | *)
– From table (combination of tables = join)
– Where only some values
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select * from scouts
select id,name from scouts
select id,name from scouts where 1<id AND id<10
select * from scouts where 1<id AND id<10
select * from scouts where id between 1 AND 10