LECTURE9-PART2: DATA MANIPULATION IN SQL, ADVANCED SQL QUERIES AND VIEW

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1 College of Computer and Information Sciences - Information Systems Dept. LECTURE9-PART2: DATA MANIPULATION IN SQL, ADVANCED SQL QUERIES AND VIEW Ref. Chapter5 and 6 from Database Systems: A Practical Approach to Design, Implementation and Management. Thomas Connolly, Carolyn Begg. 1 IS220 / IS422 : Database Fundamentals

2 The Process of Database Design 2 Conceptual Design (ERD) Logical Design (Relational Model) Physical Design Create schema (DDL) Load Data (DML)

3 Tables in the Examples 3 Customer(custNo, custname, custst, custcity, age) Product(prodNo, prodname, proddes, price) Orders(ordNo, orddate, custno, prodno, quantity) Where custname, custst, custcity, prodname, proddes are strings orddate is date Others are numbers

4 Sample Data in Customer Table 4 custno custname custst custcity age 1 C1 Olaya St Jeddah 20 2 C2 Mains St Riyadh 30 3 C3 Mains Rd Riyadh 25 4 C4 Mains Rd Dammam 5 C5 Mains Rd Riyadh

5 Sample Data in Product Table 5 prodno prodname proddes price 100 P0 Food P1 healthy food P P3 self_raising flour,80%wheat P4 network 80x 300

6 Sample Data in Orders Table 6 ordno orddate custno prodno quantity 1 01-jan jan jan jan jan mar

7 Aggregate Functions 7 COUNT - returns the number of selected values SUM - returns the sum of selected (numeric) values AVG - returns the average of selected (numeric) values MIN - returns the minimum of selected values MAX - returns the maximum of selected values

8 Use of COUNT(column_name) 8 The COUNT(column_name) function returns the number of values (NULL values will not be counted) of the specified column Syntax SELECT COUNT(column_name) FROM table_name;

9 Use of COUNT(column_name) 9 Example 1: List the number of products in the product table SELECT count(prodno) FROM product; Example 2: List the number of product descriptions in the product table SELECT count(proddes) FROM product; COUNT(PRODNO) COUNT(PRODDES) Note: count(proddes) does not count rows that have NULL value for proddes.

10 Use of COUNT(*) 10 The COUNT(*) function returns the number of records in a table (NULL values will be counted) Syntax SELECT COUNT(*) FROM table_name;

11 Use of COUNT (*) 11 Example 1: How many products are there in the product table? SELECT count(*) FROM product; COUNT(*) Example 2: How many products are priced at 300? prod No prodnam e proddes price SELECT count(*) FROM product WHERE price =300; COUNT(*) P0 Food P1 healthy food P P3 self_raising flour,80%wh eat P4 network 80x 300 Note: count(*) also count rows that have NULL values

12 Use of COUNT(DISTINCT column_name) 12 The COUNT(DISTINCT column_name) function returns the number of distinct values of the specified column: Syntax SELECT COUNT(DISTINCT column_name) FROM table_name;

13 13 Use of COUNT(DISTINCT column_name) Example1: How many cities are the customers located in? SELECT count(distinct custcity) from customer; Example 2: How many customers ordered products since 01/01/2003? SELECT count(distinct custno) FROM orders WHERE orddate >= '01-jan-2003'; COUNT(DISTINCT CUSTNO) custno custnam e COUNT(DISTINCT CUSTCITY) custst custcity age 1 C1 Olaya St Jeddah 20 ordno orddate cust prodno 2 C2 Mains St Riyadh No 30 3 C3 1 Mains 01-jan-2003 Rd Riyadh jan C4 Mains Rd Dammam 3 01-jan C5 4 Mains 01-jan-2003 Rd Riyadh jan mar quanti y

14 14 Use of SUM The SUM() function returns the total sum of a numeric column. The MIN() function returns the smallest value of the selected column. The MAX() function returns the largest value of the selected column. The AVG() function returns the average value of a numeric column. SELECT SUM(column_name),MIN(column_name),MAX(column_name),AVG(column_name) FROM table_name; Syntax

15 15 Use of SUM Example Example 1: How many products pieces were ordered by customer 1? SELECT SUM(quantity) FROM orders WHERE custno =1; SUM(QUANTITY) ordno orddate cust No Example 2: How many orders were made by customer 1 and how many products pieces did he order? prodno 1 01-jan jan jan jan jan mar quantit y SELECT count(ordno), SUM(quantity) FROM orders COUNT(ORDNO) WHERE custno =1; SUM(QUANTITY)

16 16 Example Use of AVG, MIN and MAX Example: list the minimum, maximum and average price prodno prodnam proddes price of all products. e SELECT MIN(price), MAX(price), AVG(price) FROM product; 100 P0 Food P1 healthy food P P3 self_raising flour,80%wh eat Note: if some product's price are NULLs, then SUM and AVG do not take those products into consideration P4 network 80x 300 MIN(PRICE) MAX(PRICE) AVG(PRICE)

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18 Advanced queries (GROUP BY) 18 General Syntax of SELECT command SELECT [DISTINCT] {* [columnexpression,. } FROM TableName [WHERE condition] [GROUP BY columnlist] [HAVING condition] [ORDER BYcolumnList] Order of the clauses cannot be changed. Only SELECT and FROM are mandatory

19 The GROUP BY Statement 19 The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns. Syntax SELECT column_name, aggregate_function(column_name) FROM table_name WHERE condition GROUP BY column_name;

20 Use of GROUP BY 20 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.

21 21 Example 1 ( use of group by ) O_Id OrderDate OrderPrice Customer Orders /11/ Nora /10/ Sara /09/ Nora /09/ Nora /08/ Yara /10/ Sara Nora Sara Yara find the total (total order) of each customer. use the GROUP BY statement to group the customers. SELECT Customer, SUM(OrderPrice) FROM Orders GROUP BY Customer;

22 22 Example 1 The result ( output ): what happens if we omit the GROUP BY statement SELECT Customer,SUM(OrderPrice) FROM Orders; The result Customer SUM(OrderPrice) Nora 2000 Sara 1700 Yara 2000 Customer SUM(OrderPrice) Nora 5700 Sara 5700 Nora 5700 Nora 5700 Yara 5700 Sara 5700

23 Example 2 23 List the quantity of each product ordered during Jan ordno orddate custno prodno quantity 1 01-jan SELECT prodno, sum(quantity) FROM orders WHERE orddate>='01-jan-2003' AND orddate<'01-feb-2003' GROUP BY prodno; 2 02-jan jan jan jan mar PRODNO SUM(QUANTITY)

24 24 Example 3 return the minimum and maximum salaries for each department in the employees table Employee No. First Name Last Name Dept Number Salary E1 Mandy Smith D E2 Daniel Hodges D E3 Shaskia Ramanthan D E4 Graham Burke D E5 Annie Nguyen D D2 D1 SELECT deptnumber, MIN(salary), MAX (salary) FROM employees GROUP BY deptnumber ORDER BY deptnumber; DEPTNUMBER MIN(SALARY) MAX(SALARY) D D

25 Example 4 Grouping Output from Queries 25 Example 1 : no grouping SELECT count(*) FROM EMPLOYEE; Employee No. First Name Last Name Dept Number Salary E1 Mandy Smith D E2 Daniel Hodges D E3 Shaskia Ramanthan D E4 Graham Burke D E5 Annie Nguyen D COUNT(*) Without group by COUNT(*) returns the number of rows in the table

26 Grouping Output from Queries 26 Example 2 : group by SELECT deptnumber, count(*) FROM EMPLOYEE GROUP BY deptnumber ORDER BY deptnumber; Employee No. First Name Last Name Dept Number Salary E1 Mandy Smith D E4 Graham Burke D E5 Annie Nguyen D E2 Daniel Hodges D E3 Shaskia Ramanthan D DEPTNUMBER COUNT(*) D1 3 D2 2

27 Use of HAVING 27 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. 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 ;

28 28 EXAMPLE 1 find if any of the customers have a total order of less than 2000 SELECT Customer,SUM(OrderPrice) FROM Orders GROUP BY Customer HAVING SUM(OrderPrice)<2000; O_Id OrderDate OrderPrice Customer /11/ Nora /10/ Sara /09/ Nora /09/ Nora /08/ Yara /10/ Sara CUSTOMER SUM(ORDERPRICE) SARA Without Having CUSTOMER SUM(ORDERPRICE) NORA 2000 SARA 1700 YARA 2000

29 29 Example 2 find if the customers Nora" or Yara" have a total order of more than 1500 SELECT Customer,SUM(OrderPrice) FROM Orders WHERE Customer= Nora' OR Customer= Yara' GROUP BY Customer HAVING SUM(OrderPrice)>1500 ; O_Id OrderDate OrderPrice Customer /11/ Nora /10/ Sara /09/ Nora /09/ Nora /08/ Yara /10/ Sara CUSTOMER SUM(ORDERPRICE) NORA 2000 YARA 2000

30 30 Example 3 List the product number and the quantity ordered for each product which has a total quantity of more than 2 during Jan SELECT prodno, sum(quantity) FROM orders 102 = 1 WHERE orddate>='01-jan-2003' AND orddate<'01-feb-2003' GROUP BY prodno HAVING sum(quantity)>2; ordno orddate custno prodno quantity 1 01-jan jan jan jan jan mar PRODNO SUM(QUANTITY) = 4 101=2

31 Example 4 List the department number and the total number of employee in that department for each department that has more than two employees Employee No. First Name Last Name Dept Number Salary E1 Mandy Smith D E4 Graham Burke D E5 Annie Nguyen D E2 Daniel Hodges D E3 Shaskia Ramanthan D DEPTNUMBER COUNT(*) D1 3 D2 2 SELECT deptnumber, count(*) FROM EMPLOYEE GROUP BY deptnumber HAVING count(*)>2 ORDER BY deptnumber; DEPTNUMBER COUNT(*) D1 3 31

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34 Views 34 Dynamic result of one or more relational operations operating on base relations to produce another relation. Virtual relation that does not necessarily actually exist in the database but is produced upon request, at time of request. Contents of a view are defined as a query on one or more base relations. With view resolution, any operations on view are automatically translated into operations on relations from which it is derived. With view materialization, the view is stored as a temporary table, which is maintained as the underlying base tables are updated. Pearson Education 2009

35 SQL - CREATE VIEW 35 Syntax: CREATE VIEW ViewName [ (newcolumnname [,...]) ] AS subselect [WITH [CASCADED LOCAL] CHECK OPTION] Can assign a name to each column in view. If list of column names is specified, it must have same number of items as number of columns produced by subselect. If omitted, each column takes name of corresponding column in subselect. List must be specified if there is any ambiguity in a column name. The subselect is known as the defining query. WITH CHECK OPTION ensures that if a row fails to satisfy WHERE clause of defining query, it is not added to underlying base table. Pearson Education 2009

36 Example Create Horizontal View 36 Create view so that manager at branch B003 can only see details for staff who work in his or her office. CREATE VIEW Manager3Staff AS SELECT * FROM Staff WHERE branchno = B003 ; Pearson Education 2009

37 Example Create Vertical View 37 Create view of staff details at branch B003 excluding salaries. CREATE VIEW Staff3 AS SELECT staffno, fname, lname, position, sex FROM Staff WHERE branchno = B003 ; Pearson Education 2009

38 SQL - DROP VIEW 38 Syntax: DROP VIEW ViewName [RESTRICT CASCADE] With CASCADE, all related dependent objects are deleted; i.e. any views defined on view being dropped. With RESTRICT (default), if any other objects depend for their existence on continued existence of view being dropped, command is rejected. For example: DROP VIEW Manager3Staff; Pearson Education 2009

39 View Updatability 39 All updates to base table reflected in all views that encompass base table. Similarly, may expect that if view is updated then base table(s) will reflect change. Pearson Education 2009

40 View Updatability 40 ISO specifies that a view is updatable if and only if: - DISTINCT is not specified. - Every element in SELECT list of defining query is a column name and no column appears more than once. - FROM clause specifies only one table, excluding any views based on a join, union, intersection or difference. - No nested SELECT referencing outer table. - No GROUP BY or HAVING clause. - Also, every row added through view must not Pearson Education 2009 violate integrity constraints of base table.

41 WITH CHECK OPTION 41 Rows exist in a view because they satisfy WHERE condition of defining query. If a row changes and no longer satisfies condition, it disappears from the view. New rows appear within view when insert/update on view cause them to satisfy WHERE condition. Rows that enter or leave a view are called migrating rows. WITH CHECK OPTION prohibits a row migrating out of the view. Pearson Education 2009

42 WITH CHECK OPTION 42 LOCAL/CASCADED apply to view hierarchies. With LOCAL, any row insert/update on view and any view directly or indirectly defined on this view must not cause row to disappear from view unless row also disappears from derived view/table. With CASCADED (default), any row insert/ update on this view and on any view directly or indirectly defined on this view must not cause row to disappear from the view. Pearson Education 2009

43 Example WITH CHECK OPTION 43 CREATE VIEW Manager3Staff AS SELECT * FROM Staff WHERE branchno = B003 WITH CHECK OPTION; Cannot update branch number of row B003 to B002 as this would cause row to migrate from view. Also cannot insert a row into view with a branch number that does not equal B003. Pearson Education 2009

44 Example WITH CHECK OPTION 44 Now consider the following: CREATE VIEW LowSalary AS SELECT * FROM Staff WHERE salary > 9000; CREATE VIEW HighSalary AS SELECT * FROM LowSalary WHERE salary > WITH LOCAL CHECK OPTION; CREATE VIEW Manager3Staff AS SELECT * FROM HighSalary WHERE branchno = B003 ; Pearson Education 2009

45 Example WITH CHECK OPTION 45 UPDATE Manager3Staff SET salary = 9500 WHERE staffno = SG37 ; This update would fail: although update would cause row to disappear from HighSalary, row would not disappear from LowSalary. However, if update tried to set salary to 8000, update would succeed as row would no longer be part of LowSalary. If HighSalary had specified WITH CASCADED CHECK OPTION, setting salary to 9500 or 8000 would be rejected because row would disappear from HighSalary. To prevent anomalies like this, each view should be created using WITH CASCADED CHECK OPTION. Pearson Education 2009