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Chapter 5

Structured Query Language (SQL2)

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In this lecture, you will learn:

• About more advanced queries• SQL features such as updatable views, stored

procedures, and triggers

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Four Question to Create A Query

• What output do you want to see?• What do you already know (or what constraints

are given)?• What tables are involved?• How are the tables joined together?

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Queries• Creating partial listings of table contents

SELECT <column(s)>FROM <table name>WHERE <conditions>;

Table 5.4 Mathematical Operators

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Examples

• Mathematical operators on numeric/ integer

• Mathematical operators on character attributes

• Mathematical operators on dates

SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODEFROM PRODUCTWHERE V_CODE <> 21344;

SELECT P_CODE,P_DESCRIPT,P_ONHAND,P_MIN,P_PRICEFROM PRODUCTWHERE P_CODE < ‘1558-QWI’;

SELECT P_DESCRIPT,P_ONHAND,P_MIN,P_PRICE,PINDATEFROM PRODUCTWHERE P_INDATE >= ‘01/20/2002’;

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Computed Columns

• New columns can be created through valid computations or formulas– Formulas may contain mathematical operators

– May contain attributes of any tables specified in FROM clause

• Alias is alternate name given to table or column in SQL statement

SELECT P_DESCRIPT,P_ONHAND,P_PRICE,P_ONHAND*P_PRICE AS TOTVALUE FROM PRODUCT;

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Operators

• Logical: AND, OR, NOT

• Rules of precedence– Conditions within parenthesis executed first– Boolean algebra

• Special– BETWEEN - defines limits– IS NULL - checks for nulls– LIKE - checks for similar string– IN - checks for value in a set – EXISTS - opposite of IS NULL

SELECT *FROM PRODUCTWHERE V_CODE = 21344 OR V_CODE = 24288;

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Advanced Data ManagementCommands

• ALTER - changes table structure• ADD - adds column• MODIFY - changes column characteristics

• Entering data into new column

ALTER TABLE <table name>ADD (<column name> <new column characteristics>);

ALTER TABLE <table name>MODIFY (<column name> <new column characteristics>);

UPDATE PRODUCTSET P_SALECODE = ‘2’WHERE P_CODE = ‘1546-QQ2’;

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Advanced Data Management Commands (con’t.)

• Dropping a column

• Arithmetic operators and rules of precedence

ALTER TABLE VENDORDROP COLUMN V_ORDER;

Table 5.5

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Advanced Data Management Commands (con’t.)

• Deleting a table from database

• Primary and foreign key designation

DROP TABLE PART;

ALTER TABLE LINEADD PRIMARY KEY (INV_NUMBER, LINE_NUMBER)ADD FOREIGN KEY (INV_NUMBER) REFERENCES INVOICEADD FOREIGN KEY (PROD_CODE) REFERENCES PRODUCT;

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Function Operations• COUNT

• MAX and MIN

SELECT COUNT(DISTINCT V_CODE)FROM PRODUCT;

SELECT COUNT(DISTINCT V_CODE)FROM PRODUCTWHERE P_PRICE <= 10.00;

SELECT MIN(P_PRICE)FROM PRODUCT;

SELECT P_CODE, P_DESCRIPT, P_PRICEFROM PRODUCTWHERE P_PRICE = MAX(P_PRICE);

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Example Aggregate Function Operations (con’t.)

• SUM

• AVG

SELECT SUM(P_ONHAND * P_PRICE)FROM PRODUCT;

SELECT P_DESCRIPT, P_ONHAND, P_PRICE, V_CODEFROM PRODUCTWHERE P_PRICE > (SELECT AVG(P_PRICE) FROM PRODUCT)ORDER BY P_PRICE DESC;

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More Complex Queries and SQL Functions

• Ordering a listing

• Results ascending by default– Descending order uses DESC

• Cascading order sequence

ORDER BY <attributes>

ORDER BY <attributes> DESC

ORDER BY <attribute 1, attribute 2, ...>

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More Complex Queries and SQL Functions (con’t.)

• Listing unique values– DISTINCT clause produces list of different values

• Aggregate functions– Mathematical summaries

SELECT DISTINCT V_CODE FROM PRODUCT;

Table 5.6

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More Complex Queries and SQL Functions (con’t.)

• Grouping data– Creates frequency distributions– Only valid when used with SQL arithmetic functions

– HAVING clause operates like WHERE for grouping output

SELECT P_SALECODE, MIN(P_PRICE)FROM PRODUCT_2GROUP BY P_SALECODE;

SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE)FROM PRODUCT_2GROUP BY V_CODEHAVING AVG(P_PRICE) < 10;

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More Complex Queries and SQL Functions (con’t.)

• Joining database tables– Data are retrieved from more than one table

– Recursive queries joins a table to itself

– Outer joins can be used when ‘null’ values need to be included in query result

SELECT PRODUCT.P_DESCRIPT, PRODUCT.P_PRICE, VENDOR.V_NAME, VENDOR.V_CONTACT, VENDOR.V_AREACODE, VENDOR.V_PHONEFROM PRODUCT, VENDORWHERE PRODUCT.V_CODE = VENDOR.V_CODE;

SELECT A.EMP_NUM,A.EMP_LNAME,A.EMP_MGR,B.EMP_LNAME FROM EMP A, EMP BWHERE A.EMP_MGR=B.EMP_NUMORDER BY A.EMP_MGR

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SQL JOIN (Two Table Joining)FROM table1

INNER JOIN table2

ON table1.column = table2.column

FROM table1, table2

JOIN table1.column = table2.column

SQL 92 syntax (Access and SQL Server)

Informal syntax

FROM table1, table2

WHERE table1.column = table2.column

SQL 89 syntax (Oracle & DB2)

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Syntax for Three Tables Join

FROM Table1

INNER JOIN (Table2 INNER JOIN Table3

ON Table2.ColA = Table3.ColA)

ON Table1.ColB = Table2.ColB

SQL ‘92 syntax to join three tables

FROM table1, table2, Table3

WHERE table1.column = table2.column

AND table2.column = table3.column

SQL ‘89 syntax to join three tables

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More Complex Queries and SQL Functions (con’t.)

• Virtual tables: creating a view– CREATE VIEW command– Creates logical table existing only in virtual memory

– SQL indexes

CREATE VIEW PRODUCT_3 ASSELECT P_DESCRIPT, P_ONHAND, P_PRICEFROM PRODUCTWHERE P_PRICE > 50.00;

CREATE INDEX P_CODEXON PRODUCT(P_CODE);

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Example of SQL Join

Q: List the Last Name and Phone of anyone who bought a registered White cat between 6/1/2001 and 12/31/2001.

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Example of SQL Join (con’t)• Identify the tables involved.

– Look at the columns you want to see.• LastName, Phone: Customer

– Look at the columns used in the constraints.• Registered, Color, Category: Animal

• Sale Date: Sale

– Find connector tables.• To connect from Customer to Animal, four tables involved

• Select the desired columns and test the query.• Enter the constraints.• Set Order By columns.• Add Group By columns.• Add summary computations to the SELECT statement.

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SELECT LastName, Phone FROM Customer, Animal, SaleAnimal, Sale WHERE Customer.CustomerID = Sale.CustomerID

AND Sale.SaleID = SaleAnimal.SaleID AND SaleAnimal.AnimalID = Animal.AnimalID AND Category="Cat“

AND Registered Is Not Null AND Color Like "*White*" AND SaleDate Between ‘6/1/2001’ And ‘12/31/2001’);

Example of SQL Join (con’t)

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Triggers

• Procedural SQL code invoked before or after data row is selected, inserted, or updated

• Associated within the table• Table may have multiple triggers• Invoked before or after a data row is selected,

inserted, or updated• Can update values, insert records, and call

procedures• Add processing power

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Triggers (con’t.)

• DB2 example

CREATE TRIGGER <trigger_name>[BEFORE/AFTER][DELETE/INSERT/UPDATE OF <column_name] ON <table_name>[FOR EACH ROW MODE DB2SQL]BEGIN

PL/SQL instructions;

……………END;

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Example of Trigger

Product table

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Example of Trigger (con’t)TRG_PRODUCT_REORDER

create trigger TRG_PRODUCT REORDERafter update of p_onhand, p_min on productfor each row mode db2sql update product set reorder =1 where (p_onhand <= p_min);