Chapter 7 Introduction to Structured Query Language (SQL)

Chapter 7 Introduction to Structured Query Language (SQL)
Database Systems: Design, Implementation, and Management Peter Rob & Carlos Coronel

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

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

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

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

SQL Data Definition Commands

Data Manipulation Commands

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

The Tables and Their Components The VENDOR table contains vendors who are not referenced in the PRODUCT table. PRODUCT is optional to VENDOR. Some vendors have never supplied a product ( 0,N ) 7

The Tables and Their Components Existing V_CODE values in the PRODUCT table must have a match in the VENDOR table. 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 )

The Database Model

The Chen Representation of the Invoicing Problem

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

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

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

Creating the Database Structure CREATE SCHEMA AUTHORIZATION <creator>; Example: (For most RDBMS, it is optional) CREATE SCHEMA AUTHORIZATION JONES; Schema : logical database structure a group of database objects- such as tables and indexes – that are related to each other. Refer to Ch13 in CONNOLLY’s DATABASE SYSTEMS 9

Data Dictionary Table 7.3

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

Some Common SQL Data Types

Some Common SQL Data Types
Data Type Format Numeric NUMBER(L,D) INTEGER SMALLINT DECIMAL(L,D) Character CHAR(L) VARCHAR(L) Date DATE

Creating Table Structures CREATE TABLE <table name>( <attribute1 name and attribute1 characteristics, attribute2 name and attribute2 characteristics, attribute3 name and attribute3 characteristics, primary key designation, foreign key designation and foreign key requirements>); 10

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

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

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)); 12

CREATE TABLE CUSTOMER (CUS_CODE NUMBER PRIMARY KEY, ..., ..., CUS_AREACODE CHAR(3) DEFAULT ‘615’ NOT NULL CHECK(CUS_AREACODE IN(‘615’,’713’,’931’) ), ..., ...,); 12

ON UPDATE CASCADE update V_CODE in VENDER → update V_CODE in PRODUCT
CREATE TABLE PRODUCT( P_CODE VARCHAR(10) NOT NULL UNIQUE, P_DESCRIPT VARCHAR(35) NOT NULL, P_INDATE DATE NOT NULL, P_ONHAND SMALLINT NOT NULL, P_MIN SMALLINT NOT NULL, P_PRICE DECIMAL(8,2) NOT NULL, P_DISCOUNT DECIMAL(4,1) NOT NULL, V_CODE SMALLINT, PRIMARY KEY (P_CODE), FOREIGN KEY (V_CODE) REFERENCES VENDOR ON UPDATE CASCADE); ON UPDATE CASCADE update V_CODE in VENDER → update V_CODE in PRODUCT 13

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

SQL Indexes SQL Indexes Improve the efficiency of data search
Created to meet particular search criteria CREATE INDEX P_INDATEX ON PRODUCT(P_INDATE); When the index field is a primary key whose values must not be duplicated CREATE UNIQUE INDEX P_CODEX ON PRODUCT(P_CODE); 60

A Duplicated TEST Record
Composite index Index based on two or more attributes Often used to prevent data duplication 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

Adding table rows INSERT INTO <table name> VALUES (attribute 1 value, attribute 2 value, … etc.); INSERT INTO VENDOR VALUES(‘21225, ’Bryson, Inc.’, ’Smithson’, ’615’,’ ’, ’TN’, ’Y’); INSERT INTO PRODUCT VALUES(‘11 QER/31’, ’Power painter, 15 psi., 3-nozzle’, ’03-Nov-03’, 8.5, , 0.00, 25595); 16

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

Saving table changes COMMIT [WORK]; COMMIT; Will permanently save any changes made to any table in the database Any changes made to the table contents are not physically saved on disk until Database is closed Program is closed COMMIT command is used 18

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

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

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

Listing Table Rows

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

Updating 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’; 21

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

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

Deleting Table Rows DELETE FROM PRODUCT WHERE P_CODE = ‘2238/QPD’; DELETE FROM PRODUCT WHERE P_MIN = 5; 22

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

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

SELECT Queries Selected 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

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

SELECT Queries Using Comparison Operators on Dates
SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE, P_INDATE FROM PRODUCT WHERE P_INDATE >= ‘20-Jan-2006’;

SELECT Queries SELECT Statement with a Computed Column
New columns can be created through valid expressions Formulas may contain mathematical operators 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 SELECT Statement with a Computed Column and an Alias
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 Arithmetic Operators: The Rule of Precedence
Perform operations within parentheses Perform power operations Perform multiplications and divisions Perform additions and subtractions

SELECT Queries Logical Operators: 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 PRODUCT WHERE V_CODE = OR V_CODE = 24288;

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

SELECT Queries Logical Operator: AND
SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE P_PRICE<50 AND P_INDATE>‘15-Jan-2004’;

SELECT Queries SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE (P_PRICE<50 AND P_INDATE>’15-Jan-2004’) OR V_CODE=24288;

SELECT Queries Special Operators
BETWEEN - used to define range limits. IS NULL - used to check whether an attribute value is null LIKE - used to check for similar character strings. IN - used to check whether an attribute value matches any value within a value list. EXISTS - used to check if a subquery returns any rows or not the opposite of IS NULL. 31

BETWEEN is used to define range limits. SELECT * FROM PRODUCT WHERE P_PRICE BETWEEN AND ; SELECT * FROM PRODUCT WHERE P_PRICE>=50.00 AND P_PRICE<=100.00; 31

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; 32

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%’; % : cn , c=any character, n≧0 _ : c1 33

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); 35

SELECT Queries EXISTS used to check if a subquery returns any rows or not . SELECT * FROM VENDER WHERE EXISTS (SELECT * FROM PRODUCT WHERE P_QOH <= P_MIN AND VENDER.V_CODE = PRODUCT.V_CODE); P_QOH : Quantity On Hand

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

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

Changing a Column’s Data Characteristics
Use ALTER to change data characteristics ALTER TABLE PRODUCT MODIFY (P_PRICE DECIMAL(9,2)); If 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
Use ALTER to add a column ALTER TABLE PRODUCT ADD (P_SALECODE CHAR(1)); Use ALTER to drop a column ALTER TABLE VENDOR DROP COLUMN V_ORDER; Some RDBMSs impose restrictions on the deletion of an attribute

Advanced Data Updates The Effect of Data Entry into the New P_SALECODE Column UPDATE PRODUCT SET P_SALECODE = ‘2’ WHERE P_INTADE < ’25-Dec-2005’;

Advanced Data Updates Update of the P_SALECODE Column in Multiple Data Rows UPDATE PRODUCT SET P_SALECODE = ‘1’ WHERE P_INTADE >= ’16-Jan-2006’ AND P_INTADE <= ’10-Feb-2006’;

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-2005’; UPDATE PRODUCT SET P_SALECODE = ‘1’ WHERE P_INDATE >= ‘16-Jan-2006’ AND P_INDATE < ‘10-Feb-2006’; 40

Advanced Data Updates

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

Copying Parts of Tables
Need not be identical: Column names Number of columns Column characteristics must match CREATE TABLE PART PART_CODE CHAR(8) NOT NULL UNIQUE, PART_DESCRIPT CHAR(35), PART_PRICE DECIMAL(8,2), PRIMARY KEY(PART_CODE)); INSERT INTO PART (PART_CODE,PART_DESCRIPT,PART_PRICE) SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT; 42

PART Attributes Copied from the PRODUCT Table

Adding Primary and Foreign Key Designations
For reestablish the integrity rules Forgot to define 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; 45

Deleting a Table from the Database
DROP TABLE <table name>; DROP TABLE PART; 44

Advanced Select Queries
Ordering a Listing ORDER BY <attributes> SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE FROM PRODUCT ORDER BY P_PRICE; 46

Selected PRODUCT Table Attributes: Ordered by (Ascending) P_PRICE

Partial Listing of EMPLOYEE Table Contents

Cascading order sequence
SELECT EMP_LNAME,EMP_FNAME,EMP_INITIAL,EMP_AREACODE,EMP_PHONE FROM EMPLOYEE ORDER BY EMP_LNAME, EMP_FNAME, EMP_INITIAL; 50

Descending order SELECT P_CODE, P_DESCRIPT, P_INDATE, P_PRICE FROM PRODUCT WHERE P_INDATE<‘ ’ AND P_PRICE<=50.00 ORDER BY V_CODE, P_PRICE DESC; 51

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

Aggregate Functions

COUNT SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT;

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

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

AVG 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.

Grouping Data - GROUP BY
SELECT P_SALECODE, MIN(P_PRICE) FROM PRODUCT GROUP BY P_SALECODE; 58

GROUP BY clause SELECT V_CODE, COUNT(DISTINCT(P_CODE))
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; Otherwise, you will generate a “not a GROUP BY expression” error. SELECT V_CODE, P_CODE, P_DESCRIPT, P_PRICE

Incorrect and Correct Use of the GROUP BY Clause
ERROR

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

An Application of the HAVING Clause

Virtual Tables: Creating a View
A virtual table based on a SELECT query Logical table exists only in memory Can be treated as though it were a real table CREATE VIEW PRICEGT50 AS SELECT P_DESCROPT, P_ONHAND, P_PRICE FROM PRODUCT WHERE P_PRICE > 50.00; SELECT * FROM PRICEGT50; 59

Virtual Tables: Creating a View

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

Creating Links Through Foreign Keys

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; 61

An Ordered and Limited Listing After a JOIN
SELECT 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-2006’ ORDER BY P_PRICE ;

Joining Tables With a Alias
SELECT 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 An alias is especially useful when a table must be joined to itself in a recursive query. Generate 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
Recursive Joins The Contents of the EMP Table

Using an Alias to Join a Table to Itself
manager’s names

Left Outer Join Show 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;

Left Outer Joins

Right Outer Join Show 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;

Right Outer Joins

Summary SQL commands can be divided into two overall categories:
Data definition language commands Data manipulation language commands The ANSI standard data types are supported by all RDBMS vendors in different ways Basic data definition commands allow you to create tables, indexes, and views

Summary (continued) DML commands allow you to add, modify, and delete rows from tables The basic DML commands are SELECT, INSERT, UPDATE, DELETE, COMMIT, and ROLLBACK INSERT command is used to add new rows to tables SELECT statement is main data retrieval command in SQL

Summary (continued) Many SQL constraints can be used with columns
The column list represents one or more column names separated by commas WHERE clause can be used with SELECT, UPDATE, and DELETE statements to restrict rows affected by the DDL command

Summary (continued) Aggregate functions ORDER BY clause
Special functions that perform arithmetic computations over a set of rows ORDER BY clause Used to sort output of SELECT statement Can sort by one or more columns and use either an ascending or descending order Join output of multiple tables with SELECT statement

Summary (continued) Natural join uses join condition to match only rows with equal values in specified columns Right outer join and left outer join used to select rows that have no matching values in other related table

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

The Ch06_Artist Database ERD and Tables
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A Data Dictionary for the Ch06_Artist Database
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A Summary of Foreign Key Rules
M:N Relationships Foreign key location: Composite entity 略去不講

1:M Relationships Foreign key location: Many side Foreign key 略去不講 1 M exhibit GALLERY PAINING

略去不講

Procedural language (CH7 Advanced SQL)
A 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. Common procedural languages include Basic, Pascal, C. Declarative 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. The most common examples of declarative languages are logic programming languages such as Prolog and functional languages like Haskell. CH7 Advanced SQL

Procedural SQL Shortcomings of SQL
SQL doesn’t support execution of a stored set of procedures based on some logical condition. IF-THEN-ELSE SQL fails to support the looping operations. DO-WHILE To remedy the lack of procedural functionality in SQL PSM (Persistent Stored Module) SQL99 standard defined A block of code (containing standard SQL statements and procedural extensions) that is stored and executed at the DBMS server. Oracle implements PSMs through its procedural SQL language - Procedural SQL(PL/SQL) Chapter 7範圍：7.7(pp.359)

Procedural SQL Procedural SQL
Procedural SQL make it possible to use and store procedural code and SQL statements within the database. The procedural code is executed by the DBMS when it is invoked by the end user. End users can use PL/SQL to create: Triggers Stored procedures PL/SQL functions

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

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

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

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

Procedural SQL Syntax to create a trigger in ORACLE
CREATE OR REPLACE TRIGGER <trigger_name> [BEFORE/AFTER] [DELETE/INSERT/UPDATE OF <column_name>] ON <table_name> [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’;

4 25 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’; 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 Stored Procedures
A stored procedure is a named collection of procedural and SQL statements. Stored procedures are stored in the database and invoked by name. Stored procedures are executed as a unit.

Procedural SQL Syntax 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; Syntax to invoke a stored procedure EXEC store_procedure_name(parameter, parameter, …)

Procedural SQL Stored Procedures
DECLARE is used to specify the variables used within the procedure. Argument specifies the parameters that are passed to the stored procedure. IN / OUT indicates whether the parameter is for INPUT or OUTPUT or both. 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 PL/SQL Stored Functions
A stored function is a named group of procedural and SQL statements that returns a value. 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 7 Introduction to Structured Query Language (SQL)

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