Chapter # 7 Introduction to Structured Query Language (SQL) Part I

Transcription

1 Chapter # 7 Introduction to Structured Query Language (SQL) Part I

2 Introduction to SQL SQL functions fit into two broad categories: Data definition language Data manipulation language Basic command set has vocabulary of less than 100 words American National Standards Institute (ANSI) prescribes a standard SQL Several SQL dialects exist

3 SQL Family SQL (Structured Query Language) Data Definition Language (DDL) CREATE ALTER DROP Data Manipulation Language (DML) SELECT INSERT UPDATE DELETE Data Control Language (DCL) GRANT REVOKE

4 Data Definition Commands The database model In this chapter, a simple database with these tables is used to illustrate commands: CUSTOMER INVOICE LINE PRODUCT VENDOR Focus on PRODUCT and VENDOR tables

5 Data Definition Commands (2)

6 Creating the Database Two tasks must be completed: Create database structure Create tables that will hold end-user data First task: RDBMS creates physical files that will hold database Differs substantially from one RDBMS to another CREATE DATABASE <DATABASENAME>; CREATE TABLE states ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, state CHAR(25), population INT(9) );

7 The Database Schema Authentication DBMS verifies that only registered users are able to access database Log on to RDBMS using user ID and password created by database administrator CREATE USER IDENTIFIED BY 'password'; GRANT ALL ON db1.* TO Schema Group of database objects that are related to each other

8 Data Types Data type selection is usually dictated by nature of data and by intended use Supported data types: Number(L,D), Integer, Smallint, Decimal(L,D) Char(L), Varchar(L), Varchar2(L) Date, Time, Timestamp Real, Double, Float Interval day to hour Many other types

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10 Creating Table Structures Use one line per column (attribute) definition Use spaces to line up attribute characteristics and constraints Table and attribute names are capitalized NOT NULL specification UNIQUE specification 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 semicolon

11 Creating Table Structures (Example)

12 SQL Constraints NOT NULL constraint Ensures that column does not accept nulls UNIQUE constraint Ensures that all values in column are unique DEFAULT constraint Assigns value to attribute when a new row is added to table. The end user may, of course, enter a value other than the default value. CHECK constraint Validates data when attribute value is entered

13 SQL Constraints In this chapter, Oracle is used to illustrate SQL constraints. For example, note that the following SQL command sequence uses the DEFAULT and CHECK constraints to define the table named CUSTOMER.

14 SQL Indexes When primary key is declared, DBMS automatically creates unique index Often need additional indexes Using CREATE INDEX command, SQL indexes can be created on basis of any selected attribute Using the CREATE INDEX command, SQL indexes can be created on the basis of any selected attribute. The syntax is: CREATE [UNIQUE] INDEX indexname ON tablename(column1 [, column2])

15 SQL Indexes For example, based on the attribute P_INDATE stored in the PRODUCT table, the following command creates an index named P_INDATEX: CREATE INDEX P_INDATEX ON PRODUCT(P_INDATE); Using the UNIQUE index qualifier, you can even create an index that prevents you from using a value that has been used before. Such a feature is especially useful when the index attribute is a candidate key whose values must not be duplicated: CREATE UNIQUE INDEX P_CODEX ON PRODUCT(P_CODE);

16 Data Manipulation Commands INSERT SELECT UPDATE DELETE ROLLBACK COMMIT

17 Adding Table Rows INSERT Used to enter data into table Basic Syntax: INSERT INTO columnname VALUES (value1, value2,, valuen); Example INSERT INTO VENDORVALUES (21225,'Bryson, Inc.','Smithson','615',' ','TN','Y');

18 Adding Table Rows (2) When entering values, notice that: Row contents are entered between parentheses Character and date values are entered between apostrophes Numerical entries are not enclosed in apostrophes Attribute entries are separated by commas A value is required for each column Use NULL for unknown values INSERT INTO PRODUCTVALUES ('BRT-345','Titanium drill bit','18-oct-09', 75, 10, 4.50, 0.06, NULL);

19 Saving Table Changes Changes made to table contents are not physically saved on disk until: Database is closed Program is closed COMMIT command is used Syntax: COMMIT [WORK]; NOTE TO MS ACCESS USERS MS Access doesn't support the COMMIT command because it automatically saves changes after the execution of each SQL command. Will permanently save any changes made to any table in the database

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

21 THE END