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

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 Database Design lecture 4Ses Slide 2

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. Database Design lecture 4Ses Slide 3

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; Database Design lecture 4Ses Slide 4

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

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. Database Design lecture 4Ses Slide 6

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; Database Design lecture 4Ses Slide 7

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; Database Design lecture 4Ses Slide 8

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; Database Design lecture 4Ses Slide 9

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

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; Database Design lecture 4Ses Slide 11

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 -------------------- -------------------- 001 H01 002 H01 003 H01 004 H01 005 H01 006 H01 001 H02 002 H02 003 H02 004 H02 10 rows selected. Database Design lecture 4Ses Slide 12

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. Database Design lecture 4Ses Slide 13

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 Database Design lecture 4Ses Slide 14

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

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 Database Design lecture 4Ses Slide 16

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. Database Design lecture 4Ses Slide 17

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 Database Design lecture 4Ses Slide 18

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); Database Design lecture 4Ses Slide 19

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'; Database Design lecture 4Ses Slide 20

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. Database Design lecture 4Ses Slide 21

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); Database Design lecture 4Ses Slide 22

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. Database Design lecture 4Ses Slide 23

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) Database Design lecture 4Ses Slide 24

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