WGU D427 LECTURE NOTES – RELATIONAL DATABASES OVERVIEW AND SQL | VERIFIED STUDY | 2026 UPDATES 100% CORRECT

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WGU D427 LECTURE NOTES – RELATIONAL DATABASES
OVERVIEW AND SQL | VERIFIED STUDY | 2026 UPDATES
100% CORRECT




D427

Zybook Ch 1,2,7,8



Chapter 1 Relational Databases



1.1 Relational Model
- Database Models o Conceptual framework for database systems with three parts
 Data Structures
 Describes how data is organized
 Operations
 Manipulates data structures
 Rules
 Govern valid data
- Relational data structures o Based on set theory
 Set
 Unordered collection of elements enclosed in braces o Ex: {a,b,c}
and {c,b,a} are the same
 Tuple
 Ordered collection of elements in parentheses o Ex: (a,b,c) and
(c,b,a) are different, since tuples are ordered
o Data structure organizes data in tables:
 Table
 Has a name, fixed tuple of columns, and a varying set of rows
 Column

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 Has a name, and a data type
 Row
 Is unnamed tuple of values. Each value corresponds to a column
and belongs to the columns data type
 Data type
 Is a named set of values, from which column values are drawn
- 1.1.2: Table Rows are not ordered

Grocery

The Grocery table is set of three rows

Since sets are not ordered , the left and right tables are the same.

{ (3, apple, TRUE),

(8, orange, FALSE), (0,

lemon, FALSE) }

=

(8, orange, FALSE)

(0, lemon, FALSE)

(3, apple, TRUE)



- 1.1.2: Similar Data Structure Terms
Databas Mathemati Files
es cs


Table Relation File


Column Attribute Field


Row Tuple Record


Data type Domain Data type

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- Query
o Can select a s specific row by one or more row values
- 1.1.3 Relational Data Structure o Based on set theories
o Each operation generates a result table from one or two input tables:
 Select
 Selects a subset of rows of table
 Project
 Eliminates one or more columns of table
 Product
 Lists all combinations of rows of two tables
 Join
 Combines two tables by comparing related columns
 Union
 Selects all rows of two tables
 Intersect
 Selects rows common to two tables
 Difference
 selects rows that appear in one table but not another
 Rename
 Changes a table name
 Aggregate
 Computes functions over multiple table rows, such as sum and
count
o These operations are collectively called relational algebra and are the theoretical
function of the SQL language




- 1.1.4 Relational operations and SQL Select

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SELECT *
FROM Employee
WHERE Salary > 50000;

Select* Selects all columns in the Employee table

The select Operation selects only rows for which the salary is
>50000




Project

SELECT Name

FROM Employee;

The Project operation selects only the Name column




Product

SELECT *

FROM Employee, Department;

The Product Operation selects all combinations of Employee and Department
rows



Join

SELECT *

From Employee, Department

Where Employee.DeptCode =

Department.DeptCode;

The Join operation combines Employee and Department by
comparing the tables’ DeptCode columns

- 1.16: Business rule example o Rules are logical constraint that ensure data is valid
o Relational rules