structured query language (sql)

1SQLBUAD/American University

Structured Query Language (SQL)



• SQL (pronounced "ess-que-el") stands for Structured Query Language.

• SQL is used to communicate with a database. According to ANSI (American National Standards Institute),

• it is the standard language for relational database management systems.

• SQL statements are used to perform tasks such as update data on a database, or retrieve data from a database



• Common relational database management systems that use SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc.

• most database systems use SQL, most of them also have their own additional proprietary extensions that are usually only used on their system.

• Standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" can be used to accomplish almost everything that one needs to do with a database


History of SQL

• “Sequel” project was initiated by IBM Research Lab in San Jose : 1974-79

• First RDBMS to implement SQL: SQL/DS• Other products: INGRES, Oracle, Sybase,

Informix• ISO and ANSI ratified SQL92 standard -> SQL3• Implemented in both mainframe and client/server


Benefits of a Standardized Relational Language

• Reduced training costs.

• Productivity.

• Application portability.

• Application longevity.

• Reduced dependence on a single vendor.

• Cross-system communication.


Terminology

• Data Definition Language (DDL):– Commands that define a database, including creating,

altering, and dropping tables and establishing constraints.

• Data Manipulation Language (DML)– Commands that maintain and query a database.

• Data Control Language (DCL)– Commands that control a database, including

administering privileges and committing data.


Simple SELECT statements

• query the database and retrieve selected data that match the criteria that you specify.

• format of a simple select statement:

select "column1"[,"column2",etc] from "tablename"• [where "condition"]; [] = optional


Select Command Description

• The column names that follow the select keyword determine which columns will be returned in the results. You can select as many column names that you'd like, or you can use a "*" to select all columns.

• *The table name that follows the keyword from specifies the table that will be queried to retrieve the desired results.

• *The where clause (optional) specifies which data values or rows will be returned or displayed, based on the criteria described after the keyword where.


Conditional selections used in where clause:

• = Equal

• > Greater than

• < Less than

• >= Greater than or equal to

• <= Less than or equal to

• <> Not equal to

• LIKE


Like

• Pattern matching operator can also be used in the conditional selection of the where clause.

• Selects only rows that are "like" what you specify.

• Percent sign "%" can be used as a wild card to match any possible character that might appear before or after the characters specified. For example:

• Select first, last, city from empinfo• where first LIKE 'Er%'; • This SQL statement will match any first names that start

with 'Er'. Strings must be in single quotes.


Simple Select

Retrieve the record for Team 20.SELECT *

FROM TEAMS

WHERE TEAMNUM=20;20 Yankees New York Simpson


Defining a Database

• CREATE DATABASE databasename

• CREATE TABLE tablename (column_name datatype [NULL|NOT NULL][column_contraint_clause]... column_name datatype [NULL|NOT NULL][column_contraint_clause]);


Constraint Clause

• CONSTRAINT constraint_name [PRIMARY KEY primary_key|FOREIGN KEY foreign_key REFERENCES primary_key]

• Establishes referential integrity between two tables


Modifying Table Structure

• ALTER TABLE table_name ADD (column_name data_type) … (column_name data_type) )

• Removing Table: DROP TABLE table_name


Inserting, Updating, and Deleting Data

• INSERT INTO table_name VALUES (column1_value, column2_value … )

• To delete all rows: DELETE FROM table_name

• UPDATE table_name SET column_name = new_column_value


Processing operations

• Selection: selection of a subset of rows in table(s)

• Projection: selection of a subset of columns from table(s)

• Join: joining of columns from 2 or more tables based on a certain condition

• Result of the above operations is a “relation”


Processing Single Tables

• SELECT: list of columns from base tables to be projected in to the result table

• FROM: identifies the table from which columns will be chosen to appear in the result table

• WHERE: includes the conditions for row selection within a singe table – conditions can be simple or a combination


Retrieve Table

Retrieve the entire Teams table.SELECT *

FROM TEAMS;12 Dodgers Los Angeles Wilson

15 Giants San Francisco Johnson

20 Yankees New York Simpson

24 Tigers Detroit Corbin


Simple Project

Find the numbers and names of all of the teams.SELECT TEAMNUM, TEAMNAME

FROM TEAMS;12 Dodgers

15 Giants

20 Yankees

24 Tigers


Combination of Conditions

Which players, over 27 years old, have player numbers of at least 1000?SELECT PLAYNUM, PLAYNAME

FROM PLAYERS

WHERE AGE>27

AND PLAYNUM>=1000;1131 Johnson

5410 Smith

8366 Gomez


ANDs and ORs

Which players are over 30 years old or are less than 22 years old and have a player number less than 2000?

SELECT *

FROM PLAYERS

WHERE AGE>30

OR (AGE<22 AND PLAYNUM<2000);358 Stevens 21

523 Doe 32

8366 Gomez 33


Between

Which players are between 25 and 27 years old?SELECT PLAYNUM, PLAYNAME

FROM PLAYERS

WHERE AGE BETWEEN 25 AND 27;1779 Jones

2007 Dobbs

4280 Cohen

5410 Smith


Using Expressions

• In the selection conditions, expressions (muliplication/addition) or stored functions (sum, average, min or max) can be used

• What is the total values of product in inventory?– SELECT product_name, unit_price, on_hand,

unit_price*on_hand AS value FROM product_t


Using Function

• How many different items were ordered on order number 1004?– SELECT COUNT(*) FROM product_order_t

WHERE order_id = 1004


String Comparison

Which teams are based in Detroit?SELECT TEAMNUM, TEAMNAME

FROM TEAMS

WHERE TEAMNAME=‘Detroit’;24 Tigers


Like

Find all of the players whose last names begin with “S”. (use of wildcard)SELECT PLAYNUM, PLAYNAME

FROM PLAYERS

WHERE PLAYNAME LIKE ‘S%’;358 Stevens

5410 Smith

8093 Smith


Distinct

To list unique values

List the names of the companies that manufacture bats for the league.SELECT DISTINCT MANUF

FROM BATS;Acme

General

United

Modern


IN and NOT IN Lists

• List all customers who live in Eastern States– SELECT customer_name, city, state FROM

customer_t WHERE state IN (‘NY’, ‘NJ’, ‘MD’, ‘DC’, ‘CT’)


Processing Multiple Tables

• Multiple tables are related by a JOIN operation using foreign key referencing of primary key

• FROM: list multiple table

• WHERE: foreign_key = primary_key and other conditions for join


Simple Join

• What are the names of customers who placed orders?– SELECT customer_t.customer_name FROM

customer_t, order_t WHERE customer_t.customerid = order_t.customerid

structured query language (sql)

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