1. References: Text Chapters 8 and 9
Database Design
Lecture 4
Advanced SQL
References: Text Chapters 8 and 9
Oracle SQL Manual
Database Design lecture 4Ses Slide 1

2. General Syntax of SELECT command SELECT [DISTINCT | ALL]
Advanced queries
General Syntax of SELECT command
SELECT [DISTINCT | ALL]
{* | [columnExpression [AS newName]] [,...] }
FROM TableName [alias] [, ...]
[WHERE condition]
[GROUP BY columnList]
[HAVING condition]
[ORDER BY columnList]
Order of the clauses cannot be changed.
Only SELECT and FROM are mandatory
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3. Use GROUP BY clause to get sub-totals.
Use of GROUP BY
Use GROUP BY clause to get sub-totals.
SELECT and GROUP BY closely integrated: each item in SELECT list must be single-valued per group, and SELECT clause may only contain:
Column names in the group by clause
Aggregate functions
Constants
Expression involving combinations of the above
If WHERE is used with GROUP BY, WHERE is applied first, then groups are formed from rows satisfying condition.
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4. List the quantity of each product ordered during Jan 2003.
Example 1
List the quantity of each product ordered during Jan 2003.
SELECT prodNo, sum(quantity)
FROM orders
WHERE ordDate>='01-jan-2003'
AND ordDate<'01-Feb-2003'
GROUP BY prodNo;
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5. Example 1-continued ordNo ordDate custNo prodNo quantity 1 01-jan-2003
100 2 4 3
02-jan-2003
101 5
03-jan-2003
102 6
06-mar-2003 10
Database Design lecture 4Ses Slide 5

6. Use of HAVING
HAVING clause is designed for use with GROUP BY to restrict groups that appear in final result table.
Similar to WHERE, but WHERE filters individual rows whereas HAVING filters groups.
Column names in HAVING clause must also appear in the GROUP BY list or be contained within an aggregate function.
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7. SELECT prodNo, sum(quantity) FROM orders
Example 2
List the product number and the quantity ordered for each product which has a total order of more than 2 in Jan 2003.
SELECT prodNo, sum(quantity)
FROM orders
WHERE ordDate>='01-jan-2003'
AND ordDate<'01-Feb-2003'
GROUP BY prodNo
HAVING sum(quantity)>2;
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8. Question
Are the the following statements legal? If yes do they generate the same result?
SELECT prodNo, sum(quantity)
FROM orders
WHERE ordDate>='01-jan-2003'
HAVING prodno=100
GROUP BY prodNo;
WHERE ordDate>='01-jan-2003' and prodno=100
WHERE ordDate>='01-jan-2003' and prodno=100;
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9. SELECT prodNo, sum(quantity) FROM orders
Example 3
List the product number and the quantity ordered for each product which was ordered by two or more distinct customers since 01/01/2003.
SELECT prodNo, sum(quantity)
FROM orders
WHERE ordDate>='01-jan-2003'
HAVING count(distinct custNo)>=2
GROUP BY prodNo;
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10. Example 3 -continued ordNo ordDate custNo prodNo quantity 1
01-jan-2003
100 2 4 3 6
06-mar-2003 10
02-jan-2003
101 5
03-jan-2003
102
Database Design lecture 4Ses Slide 10

11. AS is used to give a name (alias) to a column in the result table
Use of AS – column alias
AS is used to give a name (alias) to a column in the result table
Alias rather than original column name will be displayed
In Oracle, AS is optional
In Oracle, if the alias has spaces or special characters, it has to be double quoted
SELECT prodNo, sum(quantity) AS sum,
count(distinct custNo) AS noOfCust
FROM orders
WHERE ordDate>='01-jan-2003'
HAVING count(distinct custNo)>=2
GROUP BY prodNo;
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12. Alias example SQL> column "room number" format a20
SQL> column "hotel number" format a20
SQL> select RoomNo "room number", hotelno "hotel number" from room;
room number hotel number
H01
H01
H01
H01
H01
H01
H02
H02
H02
H02
10 rows selected.
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13. Selecting from Multiple Tables (Joins)
Often two or more tables are needed at the same time to find all required data
These tables must be "joined" together
The formal JOIN operation will be explained later, basically
it computes a new table from those to be joined,
the new table contains data in the matching rows of the individual tables.
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14. SQL Examples of Joins
List customers (by customer number, name and address) who have ordered the product 100.
SELECT c.custNo, custName, custSt, custCity
FROM customer c, orders o
WHERE c.custNo=o.custNo AND prodNo=100;
ordNo
ordDate
custNo
prodNo
quantity 1
01-jan-2003
100 2
02-jan-2003
101 3
102 4 5
03-jan-2003 6
06-mar-2003 10
custNo
custName
custSt
custCity
age 1 C1
Smith St
Gold Coast 20 2 C2
Mains St
Brisbane 30 3 C3
Mains Rd 25 4 C4
Sydney 5 C5
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15. Example Find the total price of the products ordered by customer 1.
SELECT sum(price*quantity) FROM orders, product
WHERE orders.prodNo = product.prodNo AND custNo = 1;
Note: relation name or alias can be used to qualify column names when there is ambiguity.
prodNo
prodName
prodDes
price
100 P0
Food
101 P1
healthy food
102 P2
200
103 P3
self_raising flour,80%wheat
300
104 P4
network 80x
ordNo
ordDate
custNo
prodNo
quantity 1
01-jan-2003
100 2
02-jan-2003
101 3
102 4 5
03-jan-2003 6
06-mar-2003 10
Database Design lecture 4Ses Slide 15

16. Left outer Join of tables r and s
Outer Joins
The outer join of two tables is a new table which not only contains the matching rows, but also contains non-matching rows.
Left outer Join of tables r and s
keeps every tuple in the left relation r, if no matching tuple in s, pad values with nulls
Right outer join
keeps every tuple in the right relation s, if no matching tuple in r, pad values with nulls
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17. Outer Joins in Oracle SQL
Put an (+) on the potentially deficient side, ie the side where nulls may be padded.
Example: List all customers, and the products ordered if they have ordered some products.
SELECT c.custNo, o.prodNo, quantity
FROM customer c, orders o
WHERE c.custNo = o.custNo(+);
Note:
a table may be outer joined with only one other table.
Which table column to use is important, eg, in above example, do not use o.custNo in place of c.custNo in the SELECT list.
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18. Query results are tables, which can also be queried.
Nested Queries (1)
Query results are tables, which can also be queried.
SELECT *
FROM (SELECT prodNo, sum(quantity) as sum
FROM orders
GROUP BY prodNo)
WHERE sum>10;
Equivalent to
SELECT prodNo, sum(quantity) as sum
GROUP BY prodNo
HAVING sum(quantity)>10;
The inner query is referred to as a subquery
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19. Example: Find products with price more than average
Nested Queries (2)
If the query result is a single value, it can be treated as a value, and be compared with other values.
Example: Find products with price more than average
SELECT prodNo, price
FROM product
WHERE price > (SELECT AVG(price)
FROM product);
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20. List the products ordered by customers living in Brisbane.
Use of IN
List the products ordered by customers living in Brisbane.
SELECT prodNo
FROM orders
WHERE custNo IN (SELECT custNo
FROM customer
WHERE custCity ='Brisbane');
This query is equivalent to
FROM orders o, customer c
WHERE o.custNo =c.custNo AND custCity = 'Brisbane';
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21. Find all customers who have ordered some products. SELECT *
EXISTS
Find all customers who have ordered some products.
SELECT *
FROM customer c
WHERE exists (SELECT *
FROM orders o
WHERE o.custNo =c.custNo);
If the subquery is not empty, then the exists condition is true.
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22. WHERE NOT EXISTS (SELECT * FROM orders o WHERE o.custNo = c.custNo
Find all customers such that no order made by them has a quantity less than 2.
SELECT *
FROM customer c
WHERE NOT EXISTS (SELECT *
FROM orders o
WHERE o.custNo = c.custNo
AND quantity <2);
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23. Correlated and Uncorrelated Subqueries
A correlated subquery is one in which the inner query is referenced by the outer query such that the inner query may be thought being executed repeatedly
SELECT *
FROM customer c
WHERE exists (SELECT *
FROM orders o
WHERE o.custNo =c.custNo);
A uncorrelated subquery is one where the subquery can be executed independently of the outer query.
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24. Subqueries versus Joins
Subqueries can often be used in place of joins. Eg
The query
SELECT distinct c.custNo, custName, custSt, custCity
FROM customer c, orders o
WHERE c.custNo=o.custNo AND prodNo=100; may be replaced with
SELECT custNo, custName, custSt, custCity
FROM customer
WHERE custNo IN (SELECT custNo FROM orders
WHERE prodNo=100); or
FROM customer c
WHERE EXISTS (SELECT * FROM orders
WHERE prodNo=100 and custNo = c.custNo)
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25. UNION, MINUS and INTERSECT
SELECT prodNo FROM product
MINUS
SELECT prodNo FROM orders; //difference from the two queries
SELECT custNo FROM customer
WHERE custCity='Brisbane'
UNION
SELECT custNo FROM orders
WHERE prodNo=102; // union of the two queries
INTERSECT
WHERE prodNo=102; // intersect of the two queries
Database Design lecture 4Ses Slide 25