Week 4 Lecture Part 2 of 3

Structured Query Language (SQL)

Samuel Conn, FacultySuggestions for using the Lecture Slides

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In this lecture, 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

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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 SQL is the ideal DB language

Data definition language Data manipulation language

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Good Reasons to Study SQL ANSI standardization effort led to

de facto query standard for relational database

Forms basis for present and future DBMS integration efforts

Becomes catalyst in development of distributed databases and database client/server architecture

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Data Definition Commands

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

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Creating Table Structure

Tables store end-user data May be based on data dictionary

entries 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 requirement>);

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Using Domains Domain is set of permissible values for a column Definition requires:

Name Data type Default value Domain constraint or condition

CREATE DOMAIN <domain_name> AS DATA_TYPE[DEFAULT <default_value>] [CHECK (<condition>)]

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SQL Integrity Constraints

Adherence to entity integrity and referential integrity rules is crucial Entity integrity enforced automatically if

primary key specified in CREATE TABLE command sequence

Referential integrity can be enforced in specification of FOREIGN KEY

Other specifications to ensure conditions met:

• ON DELETE RESTRICT • ON UPDATE CASCADE

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Data Manipulation Commands

Common SQL Commands

Table 5.3

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Data Entry and Saving

Enters data into a table

Saves changes to disk

INSERT INTO <table name> VALUES (attribute 1 value, attribute 2 value, … etc.);

COMMIT <table names> ;

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Listing Table Contents and Other Commands Allows table contents to be listed UPDATE command makes data entry

corrections ROLLBACK command restores database

back to previous condition if COMMIT hasn’t been used

DELETE command removes table row

SELECT <attribute names> FROM <table names>;

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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 Mathematical operators on character

attributes Mathematical operators on dates

SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE 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 statementSELECT 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.) Copying parts of tables

Deleting a table from database Primary and foreign key designation

INSERT INTO <receiving table> <receiving table’s column names>SELECT <column names of the columns to be copied>FROM <contributing table name>;

DROP TABLE PART;

ALTER TABLE LINE ADD PRIMARY KEY (INV_NUMBER, LINE_NUMBER) ADD FOREIGN KEY (INV_NUMBER) REFERENCES INVOICE ADD FOREIGN KEY (PROD_CODE) REFERENCES PRODUCT;

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Example Aggregate 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_2 GROUP BY V_CODE HAVING AVG(P_PRICE) < 10;

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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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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 B WHERE A.EMP_MGR=B.EMP_NUM ORDER BY A.EMP_MGR

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Updatable Views Common operation in production environments

is use of batch routines to update master table attributes using transaction data

Overnight batch jobs Not all views are updatable Restrictions

GROUP BY expressions cannot be used Cannot use set operators---UNION, INTERSECTION,

etc. Most restrictions based on use of JOINS or group

operators in views

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Procedural SQL

SQL shortcomings Doesn’t support execution of stored procedures based on logical

condition Fails to support looping operations

Solutions Embedded SQL can be called from within procedural programming

languages Shared Code is isolated and used by all application programs. Procedural SQL (PL/SQL) stored within the database, executed by

DBMS, and invoked by the end user • Triggers • Stored procedures • PL/SQL functions

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Procedural SQL (con’t.)

Procedural SQL allows the use of procedural code and SQL statements that are stored within the database.

The procedural code is executed by the DBMS when it is invoked by the end user.

End users can use procedural SQL (PL/SQL) to create: Triggers Stored procedures PL/SQL functions

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Triggers Procedural SQL code invoked before or

after data row is selected, inserted, or updated

Associated with a database table Table may have multiple triggers Executed as part of transaction Can enforce particular constraints Automate critical actions and provide

warnings for remedial action Can update values, insert records, and

call procedures Add processing power

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Triggers (con’t.)

Oracle example 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;

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Stored Procedures Named collection of procedural and SQL

statements stored in database Invoked by name Executed as unit Invoked with EXEC

CREATE OR REPLACE PROCEDURE procedure_name (argument IN/OUT data-type, etc) IS/AS BEGIN

DECLARE variable name and data typePL/SQL or SQL statements;

END;

EXEC store_procedure_name (parameter, parameter, …)

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PL/SQL Stored Functions Named group of procedural and SQL

statements that returns a value

Invoked from within stored procedures or

triggers Cannot be invoked from within SQL

statements

CREATE FUNCTION function_name (argument IN data-type, etc)RETURN data-typeAS BEGIN

PL/SQL statements;RETURN (value); ……

END;