1. Chapter 11.1 and 11.2 Data Manipulation: Relational Algebra and SQL Brian Cobarrubia Introduction to Database Management Systems October 4, 2007

2. Agenda 11.1 – Relational Algebra
Unary Operators
Binary Operators
11.2 – Structured Query Language (SQL)
SQL Queries on a Single Table
SQL Queries on Binary‏ Operators
Subqueries

3. Relational Algebra Unary Operators
Select Operator is used to select a horizontal subset of the tuples that satisfy a selection condition from a relation
σ<selection condition> (R)
Project Operator is used to select a vertical subset of certain attributes from a relation
Π<attribute list> (R)

4. Relational Algebra Binary Operators Cartesian Product Operator
Set Theoretic Operators
Union
Intersection
Difference
Join Operators
Natural Join Operator
Equijoin Operator
Theta Join Operator
Outer Join Operator
The Divide Operator

5. Relational Algebra Binary Operators
Cartesian Product Operator is used to combine tuples from any two relations in a combinatorial fashion
Relational Algebra Syntax:
RELATION_R X RELATION_S

6. Relational Algebra Binary Operators
Set Theoretic Operators are used to combine the tuples from two relations, which are then applied to two sets, the two relations must be union compatible
Two relations (R and S) are said to be Union Compatible if they have:
The same degree (i.e. Same number of attributes)
Each pair of corresponding attributes in R and S share the same domain
The operators are Union, Intersection, and Difference
Union is denoted by R U S, it is an operator that includes all tuples that belong to either R or S or to both R and S. Duplicates are eliminated
Intersection is denoted by R ∩ S, it is an operator that includes all the tuples that are only in R and S
Difference is denoted by R – S, it is an operator that includes all tuples that are in R but not in S

7. Relational Algebra Join Operators
Join Operators specify how to relate tables in the query, it is used to combine related tuples from two relations into single tuples
In order to join the two relations R and S, they must be join compatible, which means that the join condition must involve attributes from R and S which share the same domain

8. Relational Algebra Join Operators
Natural Join Operator produces all the different combinations of the tuples from the two relations R and S that satisfy a join condition
R * <join condition> S

9. Relational Algebra Join Operators
Equijoin Operator is the most common join that produces all the combinations of tuples from R and S that satisfy a join condition with only equality comparisons, there will be duplication of the joining attributes
R [X]<join condition> S note that [X] also means
Let R be STAFF table and S be DEPT:
The resulting equijoin operation would produce:

10. Relational Algebra Join Operators
Theta Join Operator produces the combinations of tuples from R and S that satisfy a join condition which does not have to involve equality comparisons (if it did then they are called an Equijoin)
R [X]<join condition> S
Let R be the CAR relation and S be the BOAT relation if a customer wants to buy both a car and boat but doesn’t want to spend more money on a boat then a car we would use a theta join operator to give a new relation with all the possible options
CarPrice ≥ BoatPrice

11. Relational Algebra Join Operators
Outer Join Operators are Inner Join operations that only look at matching tuples from one relation to the other, attributes of tuples with no matching tuples are set to NULL
Left Outer Join is denoted by ]X|, and keeps every tuple in the left or first relation (R)
Right Outer Join is denoted by |X[, and keeps every tuple in the right or second relation (S)
Full Outer Join is denoted by ]X[, and keeps all the tuples in both the left and right relations when no matching tuples are found

12. Relational Algebra Join Operators
Outer Join examples take two relations EMPLOYEE and DEPT
Left Outer Join Right Outer Join Full Outer Join

13. Relational Algebra Divide Operator
Divide Operator returns every tuple from R that match all tuples in S; R and S must be division compatible
R ÷ S
Let R be COMPLETED and S be DBPROJECT we can get the result as

14. Structured Query Language (SQL)
Overview
SQL Queries based on a Single Table
Sample SQL Queries
Handling null values
SQL Queries based on Binary Operators
Subqueries

15. Structured Query Language (SQL)
Overview
When using SQL with Relational Algebra rows are tuples, columns are attributes, and tables are relations
One of the core components of using SQL is the SELECT statement, the basic form of the SQL SELECT statement is called a select-from-where block that contains three clauses:
SELECT <column list>
Takes the table and returns the columns listed as arguments
FROM <table list>
Produces a table from the argument given
WHERE <condition>
We can specify from this clause to search in the rows for specific value types using all the comparison operators (i.e. > ≥ = ≤ <) and different conditional operations

16. Structured Query Language (SQL)
Overview
Other useful clauses for a SELECT statement include:
GROUP BY group_by_expression
Forms groups of rows with the same value
HAVING group_condition
Filters the groups subject to some condition
ORDER BY column name(s)
Specifies the order of the output
After your SELECT statement has been written a semi-colon ‘;’ is needed at the end to close up the statement

17. Structured Query Language (SQL)
SQL Queries Based on a Single Table
We can use an asterisk (*) to denote that all columns from a table is to be selected
We can also use the logical operators AND OR and NOT with the WHERE clause to form more precise clauses
When writing a query the hierarchy order in any expression follows
The comparison operators (> ≥ = ≠ ≤ <)
= is equals <> is not equals
>= is greater than or equal to <= is less than or equal to
> Is greater than < is less than
NOT operator
AND operator
OR operator

18. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Example 1
Suppose we want to know courses that are 3 hours a week
SELECT *
FROM COURSE
WHERE COURSE.CO_HOURS = 3;

19. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Example 2
Suppose we want to know all professors who make more than $6000 a month and the professors who work in a certain department (known as code 3)
SELECT *
FROM PROFESSOR
WHERE PROFESSOR.SALARY/12 > 6000
AND PROFESSOR.PR_DPT_DCODE = 3;

20. Structured Query Language (SQL)
SQL Queries Based on a Single Table
We can also simulate a projection operation by using SELECT
We can get all the colleges of a university from the co_college column with this command
SELECT COURSE.CO_COLLEGE
FROM COURSE;

21. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Other operations to use and play with
BETWEEN
Used to search for rows in a specific range of values
LIKE
Used to search for a pattern in strings
IN and NOT IN
IN is evaluated in the context of being “equal to any member of” a set of values
TRUNC
Truncates a decimal value
ROUND
Rounds a decimal value
DISTINCT
Gets rid of duplicate rows

22. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Aggregate functions take a set of values as input and returns one value as output
Common Aggregate functions are:
COUNT(x)
Counts the number of non-null values in a set of values
SUM(x)
Sums all numbers in a set of values
AVG(x)
Computes the average of a set of numbers in a set of values
MAX(x)
Computes the maximum of a set of numbers in a set of values
MIN(x)
Computes the minimum of a set of numbers in a set of values

23. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Example 3
Suppose we want to know the number of salaries, the total salary, average salary, the maximum, and the minimum salary from all the professors
SELECT COUNT(PR_SALARY), SUM(PR_SALARY), AVG(PR_SALARY), MAX(PR_SALARY), MIN(PR_SALARY)
FROM PROFESSOR;

24. Structured Query Language (SQL)
SQL Queries Based on a Single Table
Handling null values
A data field without a value in it contains a null value, they occurs when a value is unknown and where a value is not meaningful
If you try to query a column or row with a null value then it will include those spaces even though there isn’t a value associated to it
Must use IS NULL and IS NOT NULL for comparison operators with null values
This example will display that the query returned 9 rows
SELECT TEXTBOOK.TX_PUBLISHER
FROM TEXTBOOK;

25. Structured Query Language (SQL)
SQL Queries Based on Binary Operators
To perform Binary Operations on tables we use the follow keywords combined with JOIN in the FROM clause
SELECT *
FROM R CROSS JOIN S;
INNER JOIN is used in the FROM clause when the Cartesian Product operation is accompanied by a Selection operation
SELECT R.some_column(s)
FROM R INNER JOIN S
ON some_condition;
ON clause is used to specify the join conditions

26. Structured Query Language (SQL)
SQL Queries Based on Binary Operators
To perform Set Theoretic Operators in SQL we use the following:
SELECT *
FROM R
some_set_operator
FROM S;
Where some_set_operator can be:
UNION
INTERSECT
MINUS

27. Structured Query Language (SQL)
SQL Queries Based on Binary Operators
To perform joins in SQL we use the JOIN statement and compare columns that match, we can also use the predefined joins for example in Natural Joins we can use either:
SELECT * FROM R NATURAL JOIN S
SELECT * FROM R
JOIN S USING (COLUMN_1, COLUMN_2, ...);
SELECT some_R_column
FROM SECTION JOIN S ON
some_R_column = some_S column,
...;

28. Structured Query Language (SQL)
SQL Queries Based on Binary Operators
Example 4
Take a Natural Join from two tables SECTION and TAKES with this input
SELECT *
FROM SECTION NATURAL JOIN TAKES;

29. Structured Query Language (SQL)
SQL Queries Based on Binary Operators
There is a FULL OUTER JOIN statement with the syntax
SELECT *
FROM GRAD_STUDENT FULL OUTER JOIN TAKES
ON GRAD_STUDENT.GS_ST_SID = TAKES.TK_ST_SID;

30. Structured Query Language (SQL)
Subqueries
A complete SELECT statement that is embedded within another SELECT statement is a subquery
Subqueries are used in:
The SELECT list of a SELECT statement
In the FORM clause
In the WHERE clause
In the ORDER BY clause
We can use the comparison operators in combination with the ALL or ANY operator to treat the subquery as a set of values rather than individual values

31. Structured Query Language (SQL)
Subqueries
Example 4
Displays the name and salaries of those professors who earn more than all professors in department number 3
SELECT PROFESSOR.PR_NAME, PROFESSOR.PR_SALARY
FROM PROFESSOR
WHERE PROFESSOR.PR_SALARY > ALL
(SELECT PROFESSOR.PR_SALARY
WHERE PROFESSOR.PR_DPT_DCODE = 3);

32. The End