1. Working with Tables: Join, Functions and Grouping
Dr. Bernard Chen Ph.D.
University of Central Arkansas
Fall 2008

2. RETRIEVING DATA FROM A TABLE
The main purpose of the SQL language is for querying the database
The most important statement or query is the SELECT query
 The general syntax is
SELECT columnlist
FROM tablename;

3. RETRIEVING DATA FROM A TABLE
Example:
SELECT Last, First
FROM student;

4. RETRIEVING DATA FROM A TABLE
SELECT (*)
If you want to see all columns in a table, you do not have to list them all. 
You can use character asterisk (*) in place of the column list, and all columns will be displayed in the same order as the underlying table structure. 

5. RETRIEVING DATA FROM A TABLE
RESTRICTING DATA WITH A WHERE CLAUSE
A WHERE clause is used with the SELECT query to restrict rows picked
The general syntax of the WHERE clause is
SELECT columnlist
FROM tablename
[WHERE condition(s)];

6. RETRIEVING DATA FROM A TABLE
SELECT *
FROM dept
WHERE Location = ‘Monroe’;
SELECT Lname, Fname, Salary, Deptid
FROM employee
WHERE Salary >= 50000;

7. RETRIEVING DATA FROM A TABLE
SELECT Lname, Fname, Salary, Deptid
FROM employee
WHERE Salary >= AND Salary <=25000;
WHERE Salary BETWEEN AND 25000;

8. RETRIEVING DATA FROM A TABLE
SORTING
The order of rows in a table is arbitrary.
You may want to see rows in a specific order based on a column or columns
For example, you may want to see employees in alphabetical order by their name

9. RETRIEVING DATA FROM A TABLE
The ORDER BY clause is used with the SELECT query to sort rows in a table. 
The general syntax is
SELECT columnlist
FROM tablename
[WHERE condition(s)]
[ORDER BY column|expression [ASC|DESC]];

10. RETRIEVING DATA FROM A TABLE
SELECT Last, First
FROM student
ORDER BY Last;
ORDER BY Last DESC;

11. Group Functions
The group functions perform an operation on a group of rows and return one result.
Sum ()
Finds sum of all values in a column, ignores null values.
Avg ()
Finds average of all values in a column, ignores null values.
Max ()
Finds maximum value and ignores null values.
Min ()
Finds minimum value and ignores null values.
Count(), Count(*)
Counts number of rows including nulls for *. Counts non-null values if column or expression is used as argument.

12. Group Functions SELECT SUM(Salary), AVG(Salary),
MAX(Salary), MIN(Salary)
FROM EMPLOYEE;

13. Grouping Data
The rows in a table can be divided into different groups to treat each group separately.

14. Grouping Data
The GROUP BY clause is used for grouping data. The general syntax is
SELECT column, groupfunction (column)
FROM tablename
[WHERE condition(s)]
[GROUP BY column|expression]
[ORDER BY column|expression [ASC|DESC]];

15. Grouping Data
SELECT DeptID, COUNT(*)
FROM employee
GROUP BY DeptID

16. Joins
When the required data is in more than one table, related tables are joined using a join condition.
In most cases, the common columns are the primary key in one table and a foreign key in another

17. Cartesian Product
SELECT Last, First, Name
FROM student, faculty;

18. Equijoin
The equijoin is a join with a join condition involving common columns from two tables.
Join Syntax:
SELECT columnnames
FROM tablenames
WHERE join condition(s);

19. Equijoin SELECT student.Last STUDENT, faculty.Name Faculty
FROM student, faculty
WHERE student.FacultyID =
faculty.FacultyID

20. Table Aliases SELECT s.Last STUDENT, f.Name Faculty
FROM student s, faculty f
WHERE student.FacultyID =
faculty.FacultyID

21. Multiple Joins SELECT e.Lname EMPLOYEE, d.DeptName Department,
q.QualDesc QUALIFICATION
FROM EMPLOYEE e,
Department d,
QUALIFICATION q
WHERE e.DeptID = d.DeptID AND
e.QualID = q.QualID

22. Creating a table using a subquery
You can create a table by using a nested SELECT query.
The Query will create a new table and populated it with the rows selected from the other table.
CREATE TABLE tablename AS
SELECT query

23. Creating a table using a subquery
CREATE TABLE temp AS
SELECT Employee ID, Lname, Fname, Salary
FROM employee
WHERE DeptID=20;
DESCRIBE TABLE
SELECT * FROM temp;