2. Section 2
In this section will discuss
1- Examples on last section
2- Quiz
3- Like Operator
4- Top Stmt
5- Union VS Union ALL
6- IN Operator
7- Aggregation Functions
8- Group By
9- Having
10- Difference Between Having and Where
3. Quiz (1)
• Relations:
Movie(title, year, length, inColor, studioName, producerC#)
StarsIn(movieTitle, movieYear, starName)
MovieStar(name, address, gender, birthdate)
MovieExec(name, address, cert#, netWorth)
Studio(name, address, presC#)
• Queries:
a) Find the address of MGM studios.
b) Find Sandra Bullock’s birthdate.
c) Find all the stars that appear either in a movie made in 1980 or a movie
with “Love” in the title.
d) Find all executives worth at least $10,000,000.
e) Find all the stars who either are male or live in Miami ( have Miami as a
part of their address).
4. Quiz (1) Answer
a) SELECT address FROM studio
WHERE name = ‘MGM’;
b) SELECT birthdate FROM moviestar
WHERE name = ‘Sandra Bullock’;
c) SELECT starName FROM StarsIn
WHERE movieYear = 1980 OR movieTitle LIKE ‘%Love%’;
d) SELECT name FROM MovieExec
WHERE netWorth >= 10,000,000;
e) SELECT name FROM MovieStar
WHERE gender = ‘M’ OR address LIKE ‘% Miami %’;
5. LIKE Operator
• The LIKE operator is used to search for a specified pattern in a column..
• SQL LIKE Syntax:
– SELECT column_name(s) FROM table_name
WHERE column_name LIKE pattern
Persons Table
P_ID LastName FirstName Address City
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger
Ex. Want to select persons living in city ending with "s" from "Persons" table. (%
can be used to define wildcards (missing letters in pattern))
Sol: SELECT * FROM Persons WHERE City LIKE ‘%s';
6. SELECT TOP Stmt
TOP clause is used to specify the number of records to return.
Can be useful on large tables with ‘000s of records as Returning a
large
number of records can impact on performance.
SQL TOP Syntax:
SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number
Ex : Want to select only the two first records in the table above
Sol: SELECT * FROM Persons Where RowNum<2
7. Union VS Union ALL
The UNION operator returns only distinct rows
that appear in either result,
while the UNION ALL operator returns all rows.
The UNION ALL operator does not eliminate
duplicate selected rows.
8. IN Operator Nested Queries
– SELECT Model FROM Product
WHERE ManufacturerID IN
(SELECT ManufacturerID FROM Manufacturer
WHERE Manufacturer = 'Dell')
• The nested query above will select all models from the “Product” table
manufactured by Dell:
9. Aggregation Functions
Perform calculation on a set of values and return single value.
Syntax
Select Function(column) fromtable
Name Salary
Mohamed 4000
Hassan 3000
Doaa 6000
Ahmed 4000
10. Aggregation Functions
Requirements Select Stmt Result
Average of salary Select AVG(salary) from employees; 4250
Number of Rows Select COUNT(*) from employees; 4
Distinct Salaries Select COUNT(Distinct Salary) from employees; 3
Highest Salary Select MAX(salary) from employees; 6000
Lowest Salary Select MIN(salary) from employees; 3000
Total Salaries Select SUM(salary) from employees; 17000
11. Group By Clause
The GROUP BY statement is used in conjunction with
the aggregate functions to group the result-set by one
or more columns.
12. Group By Clause
Syntax
SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
13. Example
Orders Table
O_Id Order_Date Order_Price Customers
1 2013/11/12 1000 Hansen
2 2013/03/12 1600 Nilsen
3 2013/05/02 700 Hansen
4 2013/07/09 300 Hansen
5 2013/08/01 2000 Jensen
6 2013/04/03 100 Nilsen
Now we want to find the total sum (total order) of each customer.
14. Example
Sol
SELECT Customer,SUM(Order_Price) FROM Orders
GROUP BY Customer;
Customer Sum(Order_Price)
Hansen 2000
Nilsen 1700
Jinsen 2000
PS: When using the same select stmt without Group By clause
it will fire an error.
15. Example
Ex: Sells (bar, beer, price)
Find average price for each peer.
Sol: Select Beer, AVG(Price)
From Sells Group By Beer;
Ex: Get the name of the dept and its No. of Emp that
make over 25,000$ per year.
Sol: Select department, COUNT(*) as 'Number of Employees'
From Employees
Where salary > 25000
Group by department
16. Having Clause
The HAVING clause was added to SQL because the WHERE keyword
could not be used with aggregate functions.
• Also, HAVING is used in conjunction with the SELECT clause to
specify a search condition for a group. The HAVING clause behaves
like the WHERE clause, but is applicable to groups.
Syntax:
SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value
17. Example
Ex: want to find if any of the customers have a total order of less than 2000.
Sol: SELECT Customer,SUM(OrderPrice)
FROM Orders S
GROUP BY Customer
HAVING SUM(OrderPrice)<2000
Ex: want to find if the customers “Hansen” or “Jensen” have a total
order of more than 1500.
Sol: SELECT Customer,SUM(OrderPrice) FROM Orders
WHERE Customer='Hansen' OR Customer='Jensen'
GROUP BY Customer
HAVING SUM(OrderPrice)>1500
18. Example
SELECT COUNT(*)
FROM EMPLOYEES GROUP BY ID
HAVING SALARY > 15000;
this query is illegal, because the column SALARY is not a grouping column, it
does not appear within an aggregate, and it is not within a subquery;
SELECT COUNT(*)
FROM EMPLOYEES GROUP BY ID
HAVING SUM(SALARY) > 15000;
Aggregates in the HAVING clause do not need to appear in the SELECT list
19. Diff. btw. Having & Where
1. HAVING specifies a search condition for a group or an aggregate
function used in SELECT statement. The WHERE clause specifies the
criteria which individual records must meet to be selected by a query. It
can be used without the GROUP BY clause. The HAVING clause
cannot be used without the GROUP BY clause.
2. The WHERE clause selects rows before grouping. The HAVING
clause selects rows after grouping.
3. The WHERE clause cannot contain aggregate functions. The
HAVING clause can contain aggregate functions.
