Download Chapter 1 Overview of Database Concepts

Basic SQL SELECT Statements
Introduction to Oracle9i: SQL
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Chapter Objectives
• Distinguish between an RDBMS and an
ORDBMS
• Identify keywords, mandatory clauses, and
optional clauses in a SELECT statement
• Select and view all columns of a table
• Select and view one column of a table
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Chapter Objectives
• Display multiple columns of a table
• Use a column alias to clarify the contents of
a particular column
• Perform basic arithmetic operations in the
SELECT clause
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Chapter Objectives
• Remove duplicate lists, using either the
DISTINCT or UNIQUE keyword
• Combine fields, literals, and other data
• Format output
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Relational Database Management
System (RDBMS)
An RDBMS is the software program used to
create the database and it allows you to
enter, manipulate, and retrieve data
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Object Relational Database
Management System (ORDBMS)
Same as an RDBMS except it can be used
to reference objects such as maps and object
fields
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SELECT Statement Syntax
• SELECT statements are used to retrieve
data from the database
• Syntax gives the basic structure, or rules,
for a command
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SELECT Statement Syntax
Optional clauses and keywords are shown in
brackets
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SELECT Statement Syntax
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•
•
•
SELECT and FROM clauses are required
SELECT clause identifies column(s)
FROM clause identifies table(s)
Each clause begins with a keyword
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Selecting All Data in a Table
Substitute an asterisk for the column names in a
SELECT clause
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Selecting One Column from a
Table
Enter column name in SELECT clause
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Selecting Multiple Columns from
a Table
Separate column names with a comma
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Operations Within the SELECT
Statement
• Column alias can be used for column
headings
• Perform arithmetic operations
• Suppress duplicates
• Concatenate data
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Column Alias
• List after column heading
• AS keyword is optional
• Enclose in double quotation marks:
– If it contains blank space(s)
– If it contains special symbol(s)
– To retain case
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Column Alias Example
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Arithmetic Operations
•
•
•
•
Executed left to right
Multiplication and division are solved first
Addition and subtraction are solved last
Override order with parentheses
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Example Arithmetic Operation
with Column Alias
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Suppressing Duplicates
Enter DISTINCT or UNIQUE after
SELECT keyword
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Concatenation
• Can combine data with string literal
• Use concatenation operator, ||
• Allows use of column alias
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Concatenation Example
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Purpose of Joins
• Joins are used to link tables and reconstruct
data in a relational database
• Joins can be created through:
– Conditions in a WHERE clause
– Use of JOIN keywords in FROM clause
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Cartesian Join
• Created by omitting joining condition in the
WHERE clause or through CROSS JOIN
keywords in the FROM clause
• Results in every possible row combination
(m * n)
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Cartesian Join Example:
Omitted Condition
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Cartesian Join Example:
CROSS JOIN Keywords
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Equality Join
• Links rows through equivalent data that
exists in both tables
• Created by:
– Creating equivalency condition in the WHERE
clause
– Using NATURAL JOIN, JOIN…USING, or
JOIN…ON keywords in the FROM clause
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Equality Join: WHERE Clause
Example
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Equality Join: NATURAL JOIN
Syntax: tablename NATURAL JOIN tablename
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Equality Join: JOIN…USING
Syntax: tablename JOIN tablename USING (columnname)
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Equality Join: JOIN…ON
Syntax: tablename JOIN tablename ON condition
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JOIN Keyword Overview
• Use NATURAL JOIN when tables have one
column in common
• Use JOIN…USING when tables have more than
one column in common
• Use JOIN…ON when a condition is needed to
specify a relationship other than equivalency
• Using JOIN keyword frees the WHERE clause for
exclusive use in restricting rows
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Non-Equality Joins
• In WHERE clause, use any comparison
operator other than equal sign
• In FROM clause, use JOIN…ON keywords
with non-equivalent condition
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Non-Equality Join: WHERE
Clause Example
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Non-Equality Join: JOIN…ON
Example
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Self-Joins
• Used to link a table to itself
• Requires use of column qualifier
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Self-Join: WHERE Clause
Example
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Self-Join: JOIN…ON Example
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Outer Joins //
• Use to include rows that do not have a
match in the other table
• In WHERE clause, include outer join
operator (+) next to table with missing rows
to add NULL rows
• In FROM clause, use FULL, LEFT, or
RIGHT with OUTER JOIN keywords
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Outer Join: WHERE Clause
Example
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Outer Join: OUTER JOIN
Keyword Example
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Set Operators XX
Used to combine the results of two or more
SELECT statements
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Set Operator Example
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Joining Three or More Tables
• Same procedure as joining two tables
• Will always results in one less join than the
number of tables being joined
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Joining Three or More Tables:
Example
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