January 2019
Beginner
556 pages
14h 19m
English
Content preview from Learning PostgreSQL 11 - Third Edition
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Relation
Think of a relation as a table with a header, columns, and rows. The table name and the header help in interpreting the data in the rows. Each row represents a group of related data, which points to a certain object.
A relation is represented by a set of tuples. Tuples should have the same set of ordered attributes. Attributes have a domain, that is, a type and a name:
|
customer_id |
first_name |
last_name |
|
|
|
Tuple → |
1 |
thomas |
sieh |
thomas@example.com |
|
Tuple → |
2 |
wang |
kim |
kim@example.com |
|
Attribute ↑ |
Attribute ↑ |
Attribute ↑ |
Attribute ↑ |
The relation schema is denoted by the relation name and the relation attributes. For example, customer (customer_id, first_name, last_name, and email) ...
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