Ch 7

Introduction to SQL

Learning Objectives

• The basic commands and functions of SQL

• How to use SQL for data administration (to create tables, indexes, and views)

• How to use SQL for data manipulation (to add, modify, delete, and retrieve data)

• How to use SQL to query a database to extract useful information

SQL

--a standard for relational DB--used as DDL, DML--portable

Benefits:• .reduced training costs• .enhanced productivity• .application portability• .multiple vendors• .application longevity• .cross systems communications

CREATE TABLEs:..SEE Pg 223 [RC]; ORACLE HANDOUT; and lesson 17 (BF)

• define fields

• field type

• length

• null/not null

• unique

• primary key

• foreign key

Create Statement

Format:CREATE TABLE tablename

(col name datatype col_constraints, ...

[primary key block][referential constraint]

• .• .• .);

constraints in Create table statements

Constraint clause can constrain a single column or a group of columns in a table

• It helps maintain data integrity– Primary key– Foreign key– Check conditions

Two ways to specify constraints

part of col def– (col constraint)

at the end of the table– (table constraint)

Primary key

A table can have only ONE primary key

• P.K. can not have NULL values

• for single-column primary key, it can be defined with a column

• For composite it must be defined as a constraint

WORKER (w-name, age, lodging)

Create table WORKER (w_name varchar(25) Primary key, age number, Lodging varchar(15));orCreate table WORKER (

w_name varchar(25),age number,Lodging varchar(15),primary key (name));

ENROLL(st_name, cl_name, grade)

PK is st_name, cl_name

Create table Enrollment (ST_name varchar(30) not null,

cl_name varchar(25) not null,grade smallintprimary key (st_name, cl_name));

NOTE: A concatenated (composite) PK must be defined at the END

Foreign Key: (SEE ORACLE HANDOUT AND PAGE 241 (RC), LESSON 22 (bf)

• known as referential integrity constraint

ex:

WORKER (name, age, lodging)

LODGING (lodging_name , No_of_rooms, lodging_Address)

Create table WORKER(name...

age...lodging..REFERENCES LODGING);

• will automatically reference PK of LODGING relation

or• foreign key(lodging) references LODGING(lodging_name)

CHECK constraint: lesson 22 (bf);227(RC)

format:col type CHECK (condition)

• condition is any valid expression that tests True/false.ex: if age should be between 18 & 65

Create table WORKER(name..age number check (age between 18 and 65),lodging...);

• or age...check (age > 12),• ex:• class char(20) not null check (lower(class) in ('so', 'jr', 'sn') )

Data type(see ORACLE handout)

CHAR(size)   May contain any printable character such as 'A', '3', '&', or ' ' (blanks). Maximum size: 255 characters. Default is 1 byte. Padded on right with blanks to full length of size.

VARCHAR2(size) Variable length character string having a maximum of size bytes (up to 2000). NOT padded with blanks.

NUMBER For a numeric column of up to 40 digits. May be used with or without a size designation. You may use this type for integer fields, or for fields in which you wish to insert the decimal point.

NUMBER(size) For a NUMBER column of the specified size.

NUMBER(size, d) For a NUMBER column of specified size with d digits after the decimal point. For example, NUMBER(6,2) could contain nothing larger than 9999.99 without generating an error message.

DATE The DATE data type is stored in a special internal ORACLE format that includes not just the month, day, and year, but also the hour, minute, and second. However, for most tables, you will not need to be concerned about the time. For inserting a date into a table, use the following format: '10-OCT-06'.

ex:ORDER(O#, O_date, Promised_date, C#)CUSTOMER(C#, name, address, discount)

CREATE TABLE ORDER

(ORDERNO NUMBER NOT NULL,

ORDERDATE DATE,

PROMISED_DATE DATE,

CUSTOMER_NO CHAR925) NOT NULL REFERENCES CUSTOMER,

PRIMARY KEY(ORDERNO));

Entering Data in tables: lesson 15 (BF), p230(RC) and oracle handout

Format:INSERT INTO table-name VALUES ( val1, val2, val3...)

• values must be in the same order as the cols in the table structure• char must be in single quotes• date must be in quotes and default format (see ORACLE handout)

Ex: ORDER(O#, O_date, Promised_date, C#)

Sql>insert into order values (61396,’6-jun-06', '29-jun-06',1256);

• you can also insert a NULL value in a column..col will be left empty for this row

Ex:insert into order

values(61396,'6-jun-06',null,1256);

SQL

SQL can be used to manipulate data (DML)format:Sql>SELECT col name(s)

FROM table name(s)[Where condition(s)][Group BY..][HAVING.][UNION\INTERSECT\MINUS[ORDER BY....]

Assume following tables

Customer ( Cust_numb, Cust_name, Cust_address,

cust_state,Cust_balance,Credit_limit, sales_numb)

Salesperson (Sales_numb, sales_name, Sale_add, sales_state, commission_rate,

sales)

Order (Order_numb, Order_date, Cust_numb)

Working with single table

List names and balances of each customer

Sql>Select cust_name, cust_balance

From Customer;

If you want all attributes

Sql>select * from customer;

* Is a wild card and selects everything

Remove duplicate entries

Select name of cities our customers live in

Sql>select distinct cust_state

From customer;

LOGICAL TESTS AGAINST A SINGLE VALUE:

Used with-- where clause

Creates a horizontal subsection

Mathematical operators:

=, >, >=, <, <=, <> or !=

List the name of customer whose customer number is 9833

Sql> select cust_name

From customer

Where cust_numb = 9833;

List the names of salesperson who live in MD

Sql>select sales_name From salesperson Where upper(sales_state) = ‘MD’;

Ex: give the customers who ordered before February 15, 2007.

Sql>select cust_numbFrom order where order_date <’15-Feb-2006’;

LOGICAL operators:

• And• Or• Not

List the names of salespeople who live in new york and earn more than 5% as commission

Sql>select sales_name

From salesperson

Where upper(sales_ad) = ‘NEWYORK’ AND commission_rate is > 5%

List the names of salespeople who do not live in new york and earn more than 5% as commission

Case Sensitivity test

• Upper

• Lower

SPECIAL OPERATORS

• In• Between• [not] in• [not] between

• Ex:• WHERE CITY IN ('CHICAGO','BALTIMORE','TAMPA')• WHERE AGE IN (20,21,22)

same as upper(city) =’CHICAGO’ OR upper(city) =’BALTIMORE’ OR upper(city )= ‘TAMPA’

Renaming columns with Aliases/Can do arithmetic calculations on numeric attributesuseful when doing calculations

format:Sql>select colname AS alias from table namewhere. ….

Ex: give commission of salespeople.

Sql>select sales_name, sales*commission_rate as commissionFrom salesperson;

EX:List the names of customers whose credit is greater

than 2000 but less than 10000

Credit between 2000 and 10000

Calculations

+, -, /, *, ^

Order of calculations:

Parentheses,

^,

* and /,

+ and -

Comparisons

Numeric:

Based on numeric values

Character:

Left to right based on collating sequence of the computer

Smithson > Smith

Special operator

Like

Used to find patterns

Allows you select tuples that have similar characters in strings% Any # of char.- For ONE character

List names of customers whose names end with an sSELECT cust_name FROM customerWHERE lower(cust_name) like ‘%s’;

Find the names of salesperson that have a ‘c’ followed by an ‘s’

SORTINGoutput from a query can be ordered• Must always be the last line of a query• ORDER BY colname {asc}

{desc}

default is ascending

Ex: sort all customers by state and descending order of their credit limit

Sql>select *

From customer

Order by cust_state, credit_limit desc;

Exists condition

Main querySub query

If subquery returns values , then ONLY main query is executed

FormatSelect col(s)From table nameWhere exists ( sub query);

BUILT-IN-FUNCTIONS:

MaxMinSumAvgEx:Select max(credit), cust_name from customer;Has no meaning because ename is an array and

max(salary) is a scalar; cannot associate names with max(sal)

Can not mix built-in functions with other attributes, exception with groups

Count

Used to tally number of not-null values

Format:Count (*)Count(distinct attributename)Count (all attribute name)

count the number of customer in maryland or virginiaSql> select count(*)

from customerwhere upper(cust_state) In (‘MD’, ‘VA’);

Find maximum credit limit of customer whose names contain at least one o

Select max(credit_limit), cust_num

From customer

Where upper(cust_name) like ‘%O%’;

Group By

think of grouping as categorizing: P260(RC), lesson 10(bf)

Allows grouping by rows and then calculate statistics on “groups”

group by state

Will group by state

Group by state, city

Will group by state first, then by city within state

Ex: get the maximum credit limit by state

Sql>select credit_limit, cust_state

From customer

Group by cust_state;

Condition on groups: Having clause

Having puts a condition on groupsEx: select max credit limit by state where

there are atleast two customers

Sql>select max(credit_limit), cust_stateFrom customergroup by cust_stateHaving count(*) >=2;

Copying Part of table

Allows you to break tables in parts

Two steps:

1.Create NEW table

2. Use SQL to fill up the data

Format:

Insert into target_table_name (attribute names)

From source_table

Second method

Create new table and select rows directly from source table in single query

Format:

Create table target_tablename

Select attribute names

From source_table;

Create table credit for customers

1. MethodCreate table credit(c_name char(20) primary key,C_limit number (8,2));

Insert into credit (c_name, c_limit)Select cust_name, cust_limitFrom customer;

2nd Method:Create table credit asSelect cust_name as c_name, cust_limit as c_limitFrom customer;

Altering Table structure (see ORACLE Handout), lesson 17, 247 (RC)

all changes in table structure are done thru ALTER command

• MODIFY allows changing existing column

• ADD allows adding new fields

• DROP to delete a column

Alter format:

ALTER TABLE tablename[ADD (col name...,

colname...)]orALTER TABLE tablename• [MODIFY (col name..)] orALTER TABLE tablename• [Drop (col name..)]

Rules for ADDition

can add a col anytime if not null is not specified

can add multiple col at one time

can add a NULL column in three steps:– add the col without not null– fill every row– modify col to not null

Ex: add a new column soc-sec_no to customer

alter table customeradd (soc_sec_no char(14));

step2:update table customerset soc_sec_no = ‘123-32-4444”;step 3:alter table customer

modify (soc_sec_no not null);

Changing column structure

Ex: increase credit limit to 6,2

Alter table customer

Modify (credit_limit number(6,2));

Creating views (p 262); ch 18(BF)

User’s view of data

Create [or REPLACE VIEW view-name (col name) AS

SQL query

used if this view already exists

Create a view of customers with credit limit of >5000

Create view high_limit as

select cust_name from customer where

Credit_limit >500;

COLUMN NAMES MUST BE specified if• ..column names are derived• ..two or more cols have the same name

Ex: create a view that keeps track of credit averages

Create view c_avg (cust_avg, cust_name) asSelect cust_name, avg(credit_limit)From customerGroup by cust_name);

Drop a view/advantages of views

Format:

Drop view view_name

Advantages of views:

• provide data independence

• different users can view data differently

• provide security