Chapter 6 Structured Query Language (SQL) Database Systems: Design, Implementation, and Management Peter Rob & Carlos Coronel.

Chapter 6 Structured Query Language (SQL) Database Systems: Design, Implementation, and Management Peter Rob & Carlos Coronel

In this chapter, you will learn: 4The basic commands and functions of SQL 4How SQL is used for data manipulation (to add, modify, delete, and retrieve data) 4How to use SQL to query a database to extract useful information 4How SQL is used for data administration (to create tables, indexes, and views) 4About more advanced SQL features such as updatable views, stored procedures, and triggers

Introduction to SQL 4Ideal database language u Create database and table structures u Perform basic data management chores (add, delete, and modify) u Perform complex queries to transform data into useful information

Introduction to SQL 4SQL (Structured Query Language) meets ideal database language requirements: u SQL coverage fits into two categories: l Data definition –Database objects such as tables, indexes, and views –Commands to define access rights to those database objects l Data manipulation –Includes commands to insert, update, delete, and retrieve data within the database tables

Introduction to SQL 4SQL (Structured Query Language) meets ideal database language requirements: u SQL is a Nonprocedural language u SQL is relatively easy to learn. u ANSI prescribes a standard SQL. l SQL2 : SQL-92 l SQL3 : SQL-98/99 support object-oriented data management

SQL Data Definition Commands

Data Manipulation Commands

Data Definition Commands 4The Database Model u Simple Database -- PRODUCT and VENDOR tables l Each product is supplied by only a single vendor. l A vendor may supply many products.

Data Definition Commands 4The Tables and Their Components u The VENDOR table contains vendors who are not referenced in the PRODUCT table. PRODUCT is optional to VENDOR. u Some vendors have never supplied a product ( 0,N )

Data Definition Commands 4The Tables and Their Components u Existing V_CODE values in the PRODUCT table must have a match in the VENDOR table. u A few products are supplied factory-direct, a few are made in-house, and a few may have been bought in a special warehouse sale. That is, a product is not necessarily supplied by a vendor. VENDOR is optional to PRODUCT. ( 0,1 )

PRODUCT VENDER FIGURE 6.2

The Database Model

The Chen Representation of the Invoicing Problem

Creating the Database 4Two tasks must be completed u create the database structure u create the tables that will hold the end-user data 4First task u RDBMS creates the physical files that will hold the database u Tends to differ substantially from one RDBMS to another u It is relatively easy to create a database structure, regardless of which RDBMS you use.

The Database Schema 4Authentication u Process through which the DBMS verifies that only registered users are able to access the database u Log on to the RDBMS using a user ID and a password created by the database administrator 4Schema u Group of database objects—such as tables and indexes—that are related to each other

Data Definition Commands 4Create database structure u Holds all tables and is a collection of physical files stored on disk u DBMS automatically creates tables to store metadata u Database administrator creates structure or schema l Logical group of tables or logical database l Groups tables by owner l Enforces security

Data Definition Commands 4Creating the Database Structure CREATE SCHEMA AUTHORIZATION ;  Example: CREATE SCHEMA AUTHORIZATION JONES; u Schema : logical database structure a group of database objects- such as tables and indexes – that are related to each other. CREATE DATABASE ;  Example: CREATE DATABASE CH6;

Data Dictionary Table 6.3

Data Types 4Data type selection is usually dictated by the nature of the data and by the intended use 4Pay close attention to the expected use of attributes for sorting and data retrieval purposes

Some Common SQL Data Types

NumericNUMBER(L,D) INTEGER SMALLINT DECIMAL(L,D) CharacterCHAR(L) VARCHAR(L) DateDATE Data TypeFormat

Data Definition Commands 4Creating Table Structures CREATE TABLE ( );

Creating Table Structures 4Use one line per column (attribute) definition 4Use spaces to line up the attribute characteristics and constraints 4Table and attribute names are capitalized 4Primary key attributes contain both a NOT NULL and a UNIQUE specification 4RDBMS will automatically enforce referential integrity for foreign keys 4Command sequence ends with a semicolon

Other SQL Constraints 4NOT NULL constraint u Ensures that a column does not accept nulls 4UNIQUE constraint u Ensures that all values in a column are unique 4DEFAULT constraint u Assigns a value to an attribute when a new row is added to a table 4CHECK constraint u Validates data when an attribute value is entered

Data Definition Commands CREATE TABLE VENDOR (V_CODE INTEGER NOT NULL UNIQUE, V_NAME VARCHAR(35)NOT NULL, V_CONTACT VARCHAR(15)NOT NULL, V_AREACODE CHAR(3) NOT NULL, V_PHONE CHAR(3) NOT NULL, V_STATE CHAR(2) NOT NULL, V_ORDER CHAR(1) NOT NULL, PRIMARY KEY (V_CODE));

Data Definition Commands CREATE TABLE CUSTOMER (CUS_CODE NUMBER PRIMARY KEY,...,..., CUS_AREACODE CHAR(3) DEFAULT ‘615’ NOT NULL CHECK(CUS_AREACODE IN(‘615’,’713’,’931’) ),...,...,);

FOREIGN KEYREFERENCES VENDOR CREATE TABLE PRODUCT( P_CODEVARCHAR(10) NOT NULLUNIQUE, P_DESCRIPTVARCHAR(35)NOT NULL, P_INDATEDATENOT NULL, P_ONHANDSMALLINTNOT NULL, P_MINSMALLINTNOT NULL, P_PRICEDECIMAL(8,2)NOT NULL, P_DISCOUNTDECIMAL(4,1)NOT NULL, V_CODESMALLINT, PRIMARY KEY (P_CODE), FOREIGN KEY (V_CODE) REFERENCES VENDOR ON DELETE RESTRICT ON UPDATE CASCADE); 4ON DELETE RESTRICT cannot delete a vender as long as there is a product that references that vender 4ON UPDATE CASCADE update V_CODE in VENDER → update V_CODE in PRODUCT

SQL Indexes 4When a primary key is declared, DBMS automatically creates a unique index 4Often need additional indexes 4Using the CREATE INDEX command, SQL indexes can be created on the basis of any selected attribute

4SQL Indexes u Improve the efficiency of data search u Created to meet particular search criteria CREATE INDEX P_CODEX ON PRODUCT(P_CODE); u When the index field is a primary key whose values must not be duplicated CREATE UNIQUE INDEX P_CODEX ON PRODUCT(P_CODE); SQL Indexes

A Duplicated TEST Record 4Composite index u Index based on two or more attributes u Often used to prevent data duplication u Try to enter duplicate data → Error message: ”duplicate value in index” CREATE UNIQUE INDEX EMP_TESTDEX ON TEST(EMP_NUM, TEST_CODE, TEST_DATE);

Common SQL Data Manipulation Commands

Data Manipulation Commands 4Adding table rows INSERT INTO VALUES (attribute 1 value, attribute 2 value, … etc.); INSERT INTO VENDOR VALUES(‘21225, ’Bryson, Inc.’, ’Smithson’, ’615’,’223-3234’, ’TN’, ’Y’); INSERT INTO PRODUCT VALUES(‘11 QER/31’, ’Power painter, 15 psi., 3-nozzle’, ’03-Nov-03’, 8.5, 109.99, 0.00, 25595);

A Data View and Entry Form 4End-user applications are best created with utilities to create a form-based data view and entry screen.

Data Manipulation Commands 4Saving table changes COMMIT [WORK]; COMMIT; u Any changes made to the table contents are not physically saved on disk until l Database is closed l Program is closed l COMMIT command is used

Data Manipulation Commands 4SELECT command - list table contents 4UPDATE command – modify data in the table 4ROLLBACK command - restores database back to previous condition if COMMIT hasn’t been used 4DELETE command - removes table row

Data Manipulation Commands 4Listing Table Rows u SELECT l Used to list contents of table u Syntax l SELECT columnlist FROM tablename u Columnlist represents one or more attributes, separated by commas u Asterisk ( * )can be used as wildcard character to list all attributes

Data Manipulation Commands 4Listing Table Rows SELECT * FROM PRODUCT; SELECT P_CODE, P_DESCRIPT, P_INDATE, P_ONHAND, P_MIN, P-PRICE, P_DISCOUNT, V_CODE FROM PRODUCT;

Figure 6.4 The Contents of the PRODUCT Table

Data Manipulation Commands 4Updating Table Rows u UPDATE l Modify data in a table u Syntax l UPDATE tablename SET columnname = expression [, columname = expression] [WHERE conditionlist]; u If more than one attribute is to be updated in the row, separate corrections with commas

Data Manipulation Commands 4Updating table rows UPDATE PRODUCT SET P_INDATE = ‘18-Jan-2004’ WHERE P_CODE = ‘13-Q2/P2’; UPDATE PRODUCT SET P_INDATE = ‘18-Jan-2004’, P_PRICE = 15.99, P_MIN = 10 WHERE P_CODE = ‘13-Q2/P2’;

Data Manipulation Commands 4Restoring Table Contents u ROLLBACK l Used restore the database to its previous condition l Only applicable if COMMIT command has not been used to permanently store the changes in the database u Syntax l ROLLBACK; u COMMIT and ROLLBACK only work with data manipulation commands that are used to add, modify, or delete table rows u Oracle will automatically COMMIT data changes when issuing data definition commands

Data Manipulation Commands 4Deleting Table Rows u DELETE l Deletes a table row u Syntax l DELETE FROM tablename [WHERE conditionlist ]; u WHERE condition is optional u If WHERE condition is not specified, all rows from the specified table will be deleted

Data Manipulation Commands 4Deleting Table Rows DELETE FROM PRODUCT WHERE P_CODE = ‘2238/QPD’; DELETE FROM PRODUCT WHERE P_MIN = 5;

Data Manipulation Commands 4Inserting Table Rows with a Select Subquery u INSERT l Inserts multiple rows from another table (source) l Uses SELECT subquery –Query that is embedded (or nested) inside another query –Executed first u Syntax l INSERT INTO tablename SELECT columnlist FROM tablename 4Subquery – nested query / inner query u is a query that is embedded inside another query. u Is always executed first 4INSERT INTO PRODUCT SELECT * FROM P;

SELECT Queries 4Selecting Rows with Conditional Restrictions u Select partial table contents by placing restrictions on rows to be included in output u Add conditional restrictions to the SELECT statement, using WHERE clause u Syntax l SELECT columnlist FROM tablelist [ WHERE conditionlist ] ;

SELECT Queries 4Selected PRODUCT Table Attributes for VENDOR Code 21344 SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE V_CODE = 21344;

The Microsoft Access QBE and its SQL QBE (Query By Example) query generator

Comparison Operators

 Selected PRODUCT Table Attributes for VENDOR Codes Other than 21344 SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE V_CODE <> 21344; SELECT Queries

 Selected PRODUCT Table Attributes with a P_PRICE Restriction SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE FROM PRODUCT WHERE P_PRICE <= 10; SELECT Queries

4Using Comparison Operators on Character Attributes SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE FROM PRODUCT WHERE P_CODE < ‘1558-QW1’; SELECT Queries

4Using Comparison Operators on Dates SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE, P_INDATE FROM PRODUCT WHERE P_INDATE >= ‘20-Jan-2004’; SELECT Queries

4SELECT Statement with a Computed Column u New columns can be created through valid expressions u Formulas may contain mathematical operators u May contain attributes of any tables specified in FROM clause SELECT P_DESCRIPT,P_ONHAND,P_PRICE, P_ONHAND*P_PRICE FROM PRODUCT;

SELECT Queries 4SELECT Statement with a Computed Column and an Alias u 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;

SELECT Queries 4Arithmetic Operators: The Rule of Precedence u Perform operations within parentheses u Perform power operations u Perform multiplications and divisions u Perform additions and subtractions

SELECT Queries 4Logical Operators: AND, OR, NOT 4Rules of precedence u Conditions within parenthesis executed first u Boolean algebra 4Special u BETWEEN - defines limits u IS NULL - checks for nulls u LIKE - checks for similar string u IN - checks for value in a set u EXISTS - opposite of IS NULL SELECT * FROM PRODUCT WHERE V_CODE = 21344 OR V_CODE = 24288;

4Logical Operator: OR SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE V_CODE=21344 OR V_CODE=24288; SELECT Queries

4Logical Operator: AND SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE P_PRICE ‘15-Jan-2004’ ; SELECT Queries

SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE (P_PRICE ’15-Jan-2004’) OR V_CODE=24288; SELECT Queries

4Special Operators u BETWEEN - used to define range limits. u IS NULL - used to check whether an attribute value is null u LIKE - used to check for similar character strings. u IN - used to check whether an attribute value matches any value within a value list. u EXISTS - used to check if a subquery returns any rows or not - the opposite of IS NULL.

4Special Operators BETWEEN is used to define range limits. SELECT * FROM PRODUCT WHERE P_PRICE BETWEEN 50.00 AND 100.00 ; SELECT * FROM PRODUCT WHERE P_PRICE>50.00 AND P_PRICE<100.00 ; SELECT Queries

4Special Operators IS NULL is used to check whether an attribute value is null. SELECT P_CODE, P_DESCRIPT FROM PRODUCT WHERE P_MIN IS NULL; SELECT P_CODE, P_DESCRIPT FROM PRODUCT WHERE P_INDATE IS NULL; SELECT Queries

4Special Operators LIKE is used to check for similar character strings. SELECT * FROM VENDOR WHERE V_CONTACT LIKE ‘Smith%’; SELECT * FROM VENDOR WHERE V_CONTACT LIKE ‘SMITH%’; u % : c n, c=any character, n ≧ 0 u _ : c 1 SELECT Queries

4Special Operators IN is used to check whether an attribute value matches a value contained within a (sub)set of listed values. SELECT * FROM PRODUCT WHERE V_CODE IN (21344, 24288); SELECT Queries

4EXISTS used to check if a subquery returns any rows or not. SELECT * FROM VENDER WHERE EXISTS (SELECT * FROM PRODUCT WHERE P_ONHAND <= P_MIN AND VENDER.V_CODE = PRODUCT.V_CODE );

Advanced Data Definition Commands 4All changes in the table structure are made by using the ALTER command u Followed by a keyword that produces specific change u Three options are available l ADD l MODIFY l DROP

Changing a Column’s Data Type 4ALTER can be used to change data type ALTER TABLE PRODUCT MODIFY (V_CODE CHAR(5)); 4Some RDBMSs (such as Oracle) do not permit changes to data types unless the column is empty

Changing a Column’s Data Characteristics 4Use ALTER to change data characteristics ALTER TABLE PRODUCT MODIFY (P_PRICE DECIMAL(9,2)); 4If the column to be changed already contains data, changes in the column’s characteristics are permitted if those changes do not alter the data type

Adding or Dropping a Column 4Use ALTER to add a column ALTER TABLE PRODUCT ADD (P_SALECODE CHAR(1)); 4Use ALTER to drop a column ALTER TABLE VENDOR DROP COLUMN V_ORDER; u Some RDBMSs impose restrictions on the deletion of an attribute

 The Effect of Data Entry into the New P_SALECODE Column UPDATE PRODUCT SET P_SALECODE = ‘2’ WHERE P_CODE = ‘1546-QQ2’; Advanced Data Updates

 Update of the P_SALECODE Column in Multiple Data Rows UPDATE PRODUCT SET P_SALECODE = ‘1’ WHERE P_CODE IN (‘2232/QWE’, ‘2232/QTY’); Advanced Data Updates

 The Effect of Multiple Data Updates in the PRODUCT Table (MS Access) UPDATE PRODUCT SET P_SALECODE = ‘2’ WHERE P_INDATE < ‘25-Dec-2003’; UPDATE PRODUCT SET P_SALECODE = ‘1’ WHERE P_INDATE >= ‘16-Jan-2004’ AND P_INDATE < ‘10-Feb-2004’; Advanced Data Updates

Copying Parts of Tables 4SQL permits copying contents of selected table columns so that the data need not be reentered manually into newly created table(s) u First create the PART table structure u Next add rows to new PART table using PRODUCT table rows

4Need not be identical: l Column names l Number of columns 4Column characteristics must match CREATE TABLE PART PART_CODECHAR(8) NOT NULL UNIQUE, PART_DESCRIPTCHAR(35), PART_PRICEDECIMAL(8,2), PRIMARY KEY(PART_CODE)); INSERT INTO PART (PART_CODE,PART_DESCRIPT,PART_PRICE) SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT; Copying Parts of Tables

PART Attributes Copied from the PRODUCT Table

4For reestablish the integrity rules u Forgot to define u Imported tables from a different database ALTER TABLE PRODUCT ADD PRIMARY KEY (P_CODE); ALTER TABLE PRODUCT ADD FOREIGN KEY (V_CODE) REFERENCES VENDOR; ALTER TABLE PRODUCT ADD PRIMARY KEY (P_CODE) ADD FOREIGN KEY (V_CODE) REFERENCES VENDOR; Adding Primary and Foreign Key Designations

4DROP TABLE ; DROP TABLE PART; Deleting a Table from the Database

Advanced Select Queries 4Ordering a Listing ORDER BY SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE FROM PRODUCT ORDER BY P_PRICE;

Selected PRODUCT Table Attributes: Ordered by (Ascending) P_PRICE

Partial Listing of EMPLOYEE Table Contents

4Cascading order sequence SELECT EMP_LNAME,EMP_FNAME,EMP_INITIAL,EMP_AREACODE,EMP_PHONE FROM EMPLOYEE ORDER BY EMP_LNAME, EMP_FNAME, EMP_INITIAL;

4Descending order DESC SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE FROM PRODUCT WHERE P_INDATE<‘08-20-1999’ AND P_PRICE<=50.00 ORDER BY V_CODE, P_PRICE DESC;

A Listing of Distinct (Different) V_CODE Values in the PRODUCT Table DISTINCT u SELECT DISTINCT V_CODE FROM PRODUCT;

Some Basic SQL Aggregate Functions

4COUNT DISTINCT SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT;

4MAX SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT WHERE P_PRICE = (SELECT MAX(P_PRICE) FROM PRODUCT);

4SUM SELECT SUM(P_ONHAND*P_PRICE) AS TOTVALUE FROM PRODUCT;

4AVG SELECT P_DESCRIPT, P_ONHAND, P_PRICE, V_CODE FROM PRODUCT WHERE P_PRICE > (SELECT AVG(P_PRICE) FROM PRODUCT) ORDER BY P_PRICE DESC;

Determine whether goods that have been in inventory for a certain length of time should be placed on special sale.

4Grouping Data - GROUP BY SELECT P_SALECODE, MIN(P_PRICE) FROM PRODUCT GROUP BY P_SALECODE;

GROUP BY clause 4 The GROUP BY clause is valid only when used in conjunction with one of the SQL aggregate functions: COUNT, MIN, MAX, AVG, SUM  SELECT V_CODE, COUNT(DISTINCT(P_CODE)) FROM PRODUCT_2 GROUP BY V_CODE; 4Otherwise, you will generate a “not a GROUP BY expression” error.  SELECT V_CODE, P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT_2 GROUP BY V_CODE;

Incorrect and Correct Use of the GROUP BY Clause ERROR

GROUP BY’s HAVING clause 4WHERE ( SELECT ) u Applies to columns and expressions for individual rows 4HAVING ( GROUP BY ) u Applies to the output of a GROUP BY operation 4SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE) FROM PRODUCT GROUP BY V_CODE; 4SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE) FROM PRODUCT GROUP BY V_CODE HAVING AVG(P_PRICE)<10;

An Application of the HAVING Clause

4View u A virtual table based on a SELECT query u Logical table exists only in memory u Can be treated as though it were a real table 4CREATE VIEW PRODUCT_3 AS SELECT P_DESCROPT, P_ONHAND, P_PRICE FROM PRODUCT WHERE P_PRICE > 50.00 ; SELECT * FROM PRODUCT_3 ; Virtual Tables: Creating a View

Creating a Virtual Table with the CREATE VIEW Command

Joining Database Tables 4Ability to combine (join) tables on common attributes is most important distinction between a relational database and other databases 4Join is performed when data are retrieved from more than one table at a time 4Join is generally composed of an equality comparison between the foreign key and the primary key of related tables

Creating Links Through Foreign Keys

4Joining Database Tables SELECT PRODUCT.P_DESCRIPT,PRODUCT.P_PRICE, VENDOR.V_NAME, VENDOR.V_CONTACT, VENDOR.V_AREACODE, VENDOR.V_PHONE FROM PRODUCT, VENDOR WHERE PRODUCT.V_CODE=VENDOR.V_CODE;

The Results of a Join

An Ordered and Limited Listing After a JOIN 4SELECT P_DESCRIPT, P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_PHONE FROM PRODUCT, VENDOR WHERE PRODUCT.V_CODE=VENDOR.V_CODE AND P_INDATE > ‘15-Jan-2004’ ORDER BY P_PRICE ;

Joining Tables With a Alias 4SELECT P_DESCRIPT, P_PRICE, V_NAME, V_CONTACT, V_AREACODE, V_PHONE FROM PRODUCT P, VENDOR V WHERE P.V_CODE = V.V_CODE ORDER BY P_PRICE;

Recursive Joins 4An alias is especially useful when a table must be joined to itself in a recursive query. 4Generate a list of all employees with their manager’s names. SELECT E.EMP_NUM, E.EMP_LNAME, E.EMP_MGR, M.EMP_LNAME FROM EMP E, EMP M WHERE E.EMP_MGR = M.EMP_NUM ORDER BY E.EMP_MGR;

The Contents of the EMP Table

Using an Alias to Join a Table to Itself

Left Outer Join 4Show all VENDOR rows and all matching PRODUCT rows. SELECT P_CODE, VENDOR.V_CODE, V_NAME FROM VENDOR LEFT JOIN PRODUCT ON VENDOR.V_CODE = PRODUCT.V_CODE ;

The Left Outer Join Results

Right Outer Join 4Show all PRODUCT rows and all matching VENDOR rows. SELECT P_CODE, VENDOR.V_CODE, V_NAME FROM VENDOR RIGHT JOIN PRODUCT ON VENDOR.V_CODE = PRODUCT.V_CODE ;

The Right Outer Join Results

Converting an ER Model into a Database Structure 4Requires following specific rules that govern such a conversion 4Decisions made by the designer to govern data integrity are reflected in the foreign key rules

The Ch06_Artist Database ERD and Tables

A Data Dictionary for the Ch06_Artist Database

A Summary of Foreign Key Rules 4M:N Relationships u Foreign key location: Composite entity PAINING GALLERY exhibit 1M

A Summary of Foreign Key Rules 41:M Relationships u Foreign key location: Many side PAINING GALLERY exhibit 1M Foreign key

A Summary of Foreign Key Rules

Procedural language 4A term used in contrast to declarative language to describe a language where the programmer specifies an explicit sequences of steps to follow to produce a result. 4Common procedural languages include Basic, Pascal, C. 4Declarative languages describe relationships between variables in terms of functions or inference rules and the language executor (interpreter or compiler) applies some fixed algorithm to these relations to produce a result. 4The most common examples of declarative languages are logic programming languages such as Prolog and functional languages like Haskell.

Procedural SQL 4Shortcomings of SQL u SQL doesn’t support execution of a stored set of procedures based on some logical condition. IF-THEN-ELSE u SQL fails to support the looping operations. DO-WHILE 4Solutions u Embedded SQL l SQL statements can be inserted within the procedural programming language u Shared Code l Critical code is isolated and shared by all application programs. l This approach allows better maintenance. u Procedural SQL(PL/SQL)

Procedural SQL 4Procedural SQL u Procedural SQL allows the use of procedural code and SQL statements that are stored within the database. u The procedural code is executed by the DBMS when it is invoked by the end user. u End users can use PL/SQL to create: l Triggers l Stored procedures l PL/SQL functions

Procedural SQL 4Triggers u A trigger is procedural SQL code that is automatically invoked by the RDBMS upon the occurrence of a data manipulation event. l A trigger is always invoked before or after a data row is selected, inserted, or updated. l A trigger is always associated with a database table. l Each database table may have one or more triggers. l A trigger is executed as part of the transaction that triggered it. ECA (Event-Condition-Action)

Procedural SQL u Role of triggers l Triggers can be used to enforce constraints that cannot be enforced at the design and implementation levels. l Triggers add functionality by automating critical actions and providing appropriate warnings and suggestions for remedial action. l Triggers can be used to update table values, insert records in tables, and call other stored procedures.

The Revised PRODUCT Table u If P_ONHAND( 庫存 ) <= P_MIN( 安全存量 ) set P_REORDER = “Yes”

The PRODUCT List Output in the Oracle RDBMS u in Oracle : P_REORDER = 1/0 for Yes/No

Procedural SQL 4Syntax to create a trigger in ORACLE CREATE OR REPLACE TRIGGER [BEFORE/AFTER] [DELETE/INSERT/UPDATE OF ] ON [FOR EACH ROW] BEGIN PL/SQL instructions; …………… END;

Procedural SQL  Creation of the Oracle Trigger for the PRODUCT Table CREATE OR REPLACE TRIGGER TRG_PRODUCT_REORDER AFTER INSERT OR UPDATE OF P_ONHAND ON PRODUCT BEGIN UPDATE PRODUCT SET P_REORDER = 1 WHERE P_ONHAND <= P_MIN; END;

Creation of the Oracle Trigger for the PRODUCT Table

The PRODUCT Table’s P_REORDER Field is Updated by the Trigger UPDATE PRODUCT SET P_ONHAND = 4 WHERE P_CODE = ’11QER/31’;

The P_REORDER Value Mismatch UPDATE PRODUCT SET P_MIN = 7 WHERE P_CODE = ’2232/QWE’;

 The Second Version of the PRODUCT_REORDER Trigger CREATE OR REPLACE TRIGGER TRG_PRODUCT_REORDER AFTER INSERT OR UPDATE OF P_ONHAND, P_MIN ON PRODUCT BEGIN UPDATE PRODUCT SET P_REORDER = 1 WHILE P_ONHAND <= P_MIN; END;

The Second Version of the PRODUCT_REORDER Trigger

UPDATE PRODUCT SET P_MIN = 10 WHERE P_CODE = ’23114-AA’;

The P_REORDER Flag Has Not Been Properly Set After Increasing the P_ONHAND Value UPDATE PRODUCT SET P_ONHAND = P_ONHAND + P_MIN WHERE P_CODE = ’11QER/31’; 4 25 Never reset it to 0!

 The Third Version of the PRODUCT_REORDER Trigger CREATE OR REPLACE TRIGGER TRG_PRODUCT_REORDER BEFORE INSERT OR UPDATE OF P_ONHAND, P_MIN ON PRODUCT BEGIN IF :NEW.P_ONHAND <= NEW.P_MIN THEN :NEW.P_REORDER = 1; ELSE :NEW.P_REORDER = 0; END IF; END;

The Third Version of the Product Reorder Trigger

 After creating the new trigger, we can execute an UPDATE statement to fire it. UPDATE PRODUCT SET P_ONHAND = P_ONHAND

Execution of the Third Trigger Version

Procedural SQL 4Stored Procedures u A stored procedure is a named collection of procedural and SQL statements. u Stored procedures are stored in the database and invoked by name. u Stored procedures are executed as a unit.

Procedural SQL 4Syntax to create a stored procedure CREATE OR REPLACE PROCEDURE procedure_name (argument IN/OUT data-type, etc) IS/AS BEGIN DECLARE variable name and data type PL/SQL or SQL statements; END; 4Syntax to invoke a stored procedure EXEC store_procedure_name(parameter, parameter, …)

Procedural SQL 4Stored Procedures u DECLARE is used to specify the variables used within the procedure. u Argument specifies the parameters that are passed to the stored procedure. u IN / OUT indicates whether the parameter is for INPUT or OUTPUT or both. u Data-type is one of the procedural SQL data types used in the RDBMS.

Creating and Invoking A Simple Stored Procedure

The PROD_SALE Stored Procedure CREATE OR REPLACE PROCEDURE PROD-SALE (CODE IN VARCHAR2, QTYSOLD IN NUMBER) AS BEGIN UPDATE PRODUCT SET P_ONHAND = P_ONHAND - QTYSOLD WHERE P_CODE = CODE; END;

Creation of the PROD_SALE Stored Procedure

Executing the PROD_SALE Stored Procedure

Procedural SQL 4PL/SQL Stored Functions u A stored function is a named group of procedural and SQL statements that returns a value. u Syntax to create a function: CREATE FUNCTION function_name (argument IN data-type, etc) RETURN data-type AS BEGIN PL/SQL statements; RETURN (value); …… END;

Chapter 6 Structured Query Language (SQL) Database Systems: Design, Implementation, and Management Peter Rob & Carlos Coronel.

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