An Introduction to SQL Kirk Anne Computing & Information Technology SUNY Geneseo Nael Alian

What is a database?

Parts of a database Attributes (fields) – An attribute or field is a component of a record that describes something about an item. Records – A record is the representation of an individual item. Table – A collection of records Database – A collection of tables and rules for accessing the tables

Parts of a database Record Attribute/Field Tables Records become “rows” Attributes/fields become “columns” Rules determine the relationship between the tables and tie the data together to form a database

I need a new database! Many people ask for “new databases” when in fact they only need a new table within an existing database. The data within the tables should be all related somehow. – By owner – By project

Creating a database What information are we trying to store? How do we describe the information? Phone Book/Contact entries – Name – Address – Company – Phone Number – URL/Web Page – Age – Height (in meters) – Birthday – When we added the entry

Data Types Binary – Database specific binary objects – Pictures, digital signatures, etc. Boolean – True/False values Character – Fixed width or variable size Numeric – Integer, Real (floating decimal point), Money Temporal – Time, Date, Timestamp

Phone Book/Contact Record NameCharacter AddressCharacter CompanyCharacter Phone NumberCharacter URL/Web PageCharacter AgeInteger HeightReal (float) BirthdayDate When we added the entryTimestamp

All you need to know about SQL

What is SQL? 1. SQL stands for Structured Query Language 2. SQL lets you access and manipulate databases 3. SQL is an ANSI (American National Standards Institute) standard

SQL can execute queries against a database SQL can retrieve data from a database SQL can insert records in a database SQL can update records in a database SQL can delete records from a database SQL can create new databases SQL can create new tables in a database SQL can create stored procedures in a database SQL can create views in a database SQL can set permissions on tables, procedures, and views

SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL). The query and update commands form the DML part of SQL: SELECT - extracts data from a database UPDATE - updates data in a database DELETE - deletes data from a database INSERT INTO - inserts new data into a database

The DDL part of SQL permits database tables to be created or deleted. It also define indexes (keys), specify links between tables, and impose constraints between tables. The most important DDL statements in SQL are: CREATE DATABASE - creates a new database ALTER DATABASE - modifies a database CREATE TABLE - creates a new table ALTER TABLE - modifies a table DROP TABLE - deletes a table CREATE INDEX - creates an index (search key) DROP INDEX - deletes an index

Basic SQL Commands Creating tables with CREATE Adding data with INSERT Viewing data with SELECT Removing data with DELETE Modifying data with UPDATE Destroying tables with DROP

Creating tables with CREATE Generic form CREATE TABLE tablename ( column_name data_type attributes…, … ) Table and column names can’t have spaces or be “reserved words” like TABLE, CREATE, etc.

Phone Book/Contact Record NameCharacter AddressCharacter CompanyCharacter Phone NumberCharacter URL/Web PageCharacter AgeInteger HeightReal (float) BirthdayDate When we added the entryTimestamp

Phone Book/Contact Table CREATE TABLE contacts ( NameVARCHAR(40), Address VARCHAR(60), Company VARCHAR(60), Phone VARCHAR(11), URLVARCHAR(80), AgeINT, HeightFLOAT, BirthdayDATE, WhenEnteredTIMESTAMP ); Plan your tables very carefully! Once created, they are difficult to change!

Phone Book/Contact Table CREATE TABLE contacts ( ContactIDINT PRIMARY KEY, NameVARCHAR(40), Address VARCHAR(60), Company VARCHAR(60), Phone VARCHAR(11), URLVARCHAR(80), AgeINT, HeightFLOAT, BirthdayDATE, WhenEnteredTIMESTAMP ); If you are going to use the relational nature of a database, don’t forget you need to have a unique way to access records! There is a way to make the key automatically increment, so you don’t have to worry about which one is next.

Data Types Binary – Database specific binary objects (BLOB) Boolean – True/False values (BOOLEAN) Character – Fixed width (CHAR) or variable size (VARCHAR) Numeric – Integer (INT), Real (FLOAT), Money (MONEY) Temporal – Time (TIME), Date (DATE), Timestamp (TIMESTAMP)

Create Table emp ( eno Varchar2(10) Not Null, ename Varchar2(30),age Varchar2(5) Null, salary Number(10), birth_day Date ) ; انشاء جدول يحتوي على القيم التالية اسم الحقل نوعةطولة يجب ادخال القيمة enoVarchar210not Null يجب ادخالها enameVarchar230not Null يجب ادخالها ageVarchar25 لايجب ادخالها salarynumber10 Null لايجب ادخالها birth_daydate- لايجب ادخالها

Adding data with INSERT Generic Form INSERT INTO tablename (column_name,…) VALUES (value,…)

Inserting a record into ‘contacts’ INSERT INTO contacts (contactid,name,address,company,phone,url,a ge,height,birthday,whenentered) VALUES (1,‘Joe’,’123 Any St.’,’ABC’, ’ ’,‘ ’6/14/1972’, now());

Inserting a partial record INSERT INTO contacts (contactid,name,phone) VALUES (2,’Jane’,’ ’);

Automatic key generation CREATE SEQUENCE contactidseq; Change the ContactID line in the CREATE TABLE to: ContactIDINT DEFAULT nextval(‘contactidseq’) PRIMARY KEY Or when inserting into a table INSERT contacts (contactid,name,phone) VALUES (nextval(‘contactidseq’),’Jack’, ‘ ’);

Insert Into emp (eno,ename) values ('10', 'صالح' ) اضافة البيانات التالية الى الحقول المحددة Insert Into emp (eno,ename) values (&no, '&name' ); اضافة البيانات التالية الى الحقول المحددة ويطلب القيم عند التنفيذ

Viewing data with SELECT Generic Form SELECT column,… FROM table,… WHERE condition GROUP BY group_by_expression HAVING condition ORDER BY order_expression The most used command Probably the most complicated also If used improperly, can cause very long waits because complex computations

A few simple SELECTs SELECT * FROM contacts; – Display all records in the ‘contacts’ table SELECT contactid,name FROM contacts; – Display only the record number and names SELECT DISTINCT url FROM contacts; – Display only one entry for every value of URL.

Select Distinct ename from emp ; عرض اسماء الموظفين بدون تكرار Select Distinct ename,eno from emp ; عرض اسماء الموظفين وارقامهم دون تكرار قيم حقل الاسم

Refining selections with WHERE The WHERE “subclause” allows you to select records based on a condition. SELECT * FROM contacts WHERE age<10; – Display records from contacts where age<10 SELECT * FROM contacts WHERE age BETWEEN 18 AND 35; – Display records where age is 18-35

Additional selections The “LIKE” condition – Allows you to look at strings that are alike SELECT * FROM contacts WHERE name LIKE ‘J%’; – Display records where the name starts with ‘J’ SELECT * FROM contacts WHERE url LIKE ‘%.com’; – Display records where url ends in “.com”

Select * from emp ; Emp عرض جميع بيانات الجدول Select ename from emp ; عرض اسماء الموظفين من جدول الموظفين Select salary*0.91 from emp ; عرض رواتب الموظفين مخصوم منها التقاعد 9 في المائة

Removing data with DELETE Generic Form DELETE FROM table WHERE condition; DELETE FROM contacts WHERE age<13;

Delete * from emp where eno=12 ; حذف جميع بيانات الموظف الذي رقمة 12 Delete * from emp where eno=12 ; حذف جميع بيانات الموظف الذي رقمة 12 Delete eno,name from emp where eno=12 ; حذف رقم واسم الموظف الذي رقمة 12

Modifying data with UPDATE Generic Form UPDATE table SET column=expression WHERE condition; UPDATE contacts SET company=‘AOL’ WHERE company=‘Time Warner’;

Destroying tables with DROP Generic Form DROP TABLE tablename; DROP TABLE contacts;

More about SELECT

Different types of JOINs “Inner Join” – Unmatched rows in either table aren’t printed “Left Outer Join” – All records from the “left” side are printed “Right Outer Join” – All records from the “right” side are printed “Full Outer Join” – All records are printed Multiple Table Join – Join records from multiple tables

General form of SELECT/JOIN SELECT columns,… FROM left_table join_type JOIN right_table ON condition; SELECT name,phone FROM people JOIN phonenumbers ON people.id=phonenumbers.id;

Other versions SELECT name,phone FROM people LEFT JOIN phonenumbers ON people.id=phonenumbers.id; SELECT name,phone FROM people RIGHT JOIN phonenumbers ON people.id=phonenumbers.id; SELECT name,phone FROM people FULL JOIN phonenumbers ON people.id=phonenumbers.id;

“Theta style” vs. ANSI Theta Style (used in most SQL books) SELECT name,phone,zip FROM people, phonenumbers, address WHERE people.addressid=address.addressid AND people.id=phonenumbers.id; ANSI Style uses JOIN SELECT name,phone,zip FROM people JOIN phonenumbers ON people.id=phonenumbers.id JOIN address ON people.addressid=address.addressid;

Other SELECT examples SELECT * FROM contacts WHERE name is NULL; SELECT * FROM contacts WHERE zip IN (‘14454’,’12345’); SELECT * FROM contacts WHERE zip IN ( SELECT zip FROM address WHERE state=‘NY’ );

GROUP BY/HAVING The “GROUP BY” clause allows you to group results together with “aggregate functions” – AVG(), COUNT(), MAX(), MIN(), SUM() – COUNT DISTINCT HAVING allows you to search the GROUP BY results

GROUP BY Examples SELECT company,count(company) FROM contacts GROUP BY company; SELECT company,count(company) FROM contacts GROUP BY company HAVING count(company) > 5;

ORDER BY The “ORDER BY” clause allows you to sort the results returned by SELECT. SELECT * FROM contacts ORDER BY company; SELECT * FROM contacts ORDER BY company, name;

Views You can use “CREATE VIEW” to create a virtual table from a SELECT statement. CREATE VIEW contactview AS (SELECT name,phone,zip FROM people,phonenumbers,address WHERE people.id=phonenumbers.id AND people.addressid=address.addressid);