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Results tagged with relational-theory
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user 3847
On this site this tag applies to questions about Relational Model theory. The Relational Model for database management is an approach to managing data using a structure and language consistent with first-order predicate logic. In the Relational Model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the Relational Model is a relational database.
5
votes
Accepted
Definition for "logical difference"?
See Date's book:
Date on Database: Writings 2000-2006
Chapter 4: On the Notion of Logical Difference
Salient quote:
you'll be aware that I often appeal in my writings to the notion of
logical …
- 2,622
4
votes
How to express this constraint in a database schema?
In a nutshell, introduce d into the third table to enable vanilla foreign key constraints e.g. Transitional SQL-92 syntax:
CREATE TABLE T1
(
a INTEGER NOT NULL,
d INTEGER NOT NULL,
UNIQUE (a, d) …
- 2,622
3
votes
Accepted
How to express this constraint in a database schema?
In a nutshell, create an ASSERTION to ensure that at no time can the business rule be violated e.g. Full Standard SQL-92 syntax:
CREATE TABLE T1
(
a INTEGER NOT NULL,
d INTEGER NOT NULL,
UNIQUE …
- 2,622
1
vote
How to normalize Time Sheet data?
Something like this:
Employees { Staff } KEY { Staff } ;
Clients { Client } KEY { Client } ;
StaffAssignments { Client , Staff }
KEY { Client , Staff }
FOREIGN KEY { Client } REFERENCES Cli …
- 2,622
4
votes
6th normal form, recomposition query, efficient implementation
Download Dr. Hugh Darwen's free PDF book, An Introduction to Relational Database Theory. Specifically, chapter 7 and the WIFE_OF_HENRY_VIII example. In summary, 6NF is always achievable but may not al …
- 2,622
2
votes
Express union which is dependent on other results
Do you mean intersect? Consider relvars Customers and Orders with a correspondence where one customer has zero, one or many orders (I wouldn't refer to this as a hierarchy, though). To find customers …
- 2,622