1. Subqueries

2. Based on Introduction to Oracle: SQL and PL/SQL
Problem
Solution to question
Requires a two step query
Can use only one SQL statement
Example – Who has a salary greater than Jones’ salary?
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

3. Based on Introduction to Oracle: SQL and PL/SQL
Use a Subquery
Main Query
Which employees have a salary greater than Jones’ salary?
Subquery
What is Jones’ salary?
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

4. Based on Introduction to Oracle: SQL and PL/SQL
SELECT select_list FROM table WHERE expr operator (SELECT select_list FROM table)
Subquery (bottom) executed first
Outer query (top) executed last
Addition SQL clauses
can be added
Inner & Outer queries
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

5. Based on Introduction to Oracle: SQL and PL/SQL
Types of Subqueries
Single-row subquery
Multiple-row subquery
Multiple-column subquery
Main query
Subquery
CLERK
Main query
returns
CLERK
MANAGER
Subquery
Main query
returns
Subquery
CLERK
MANAGER
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

6. Single-Row Subqueries
Return only one row to Main Query
Use single-row comparison operators
=, >, >=, <, <=, and <>
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

7. Based on Introduction to Oracle: SQL and PL/SQL
Example
Find the employee names and jobs for employees whose salary is greater than employee number 7876 and who have the same job as employee number 7369.
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

8. Multiple-Row Subqueries
Return more than one row
Use multiple-row comparison operators
IN, equal to any member in the list
ANY
ALL
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL

9. Based on Introduction to Oracle: SQL and PL/SQL
Example
Find the employee name, salary, and department number for the employee who has the minimum salary in each department.
2/24/05
Based on Introduction to Oracle: SQL and PL/SQL