Sql

SQL
Introduction to SQL
Atul Pant

Table of Contents
SQL Intro .......................................................................................................................................................3
SQL Select .....................................................................................................................................................4
SQL Select Distinct ........................................................................................................................................4
SQL Where.....................................................................................................................................................4
SQL And & Or ...............................................................................................................................................5
SQL Order By ................................................................................................................................................5
SQL Insert Into ...............................................................................................................................................5
SQL Update ....................................................................................................................................................6
SQL Delete .....................................................................................................................................................6
SQL Select Top ..............................................................................................................................................6
SQL Select Top ..............................................................................................................................................7
SQL Like ........................................................................................................................................................7
SQL Wildcards ...............................................................................................................................................7
SQL IN ...........................................................................................................................................................8
SQL Between .................................................................................................................................................8
SQL Join ........................................................................................................................................................8
SQL Inner Join ...............................................................................................................................................9
SQL Left Join .................................................................................................................................................9
SQL Right Join...............................................................................................................................................9
SQL Full Join ...............................................................................................................................................10
SQL Union ...................................................................................................................................................10
SQL Select Into ............................................................................................................................................10
SQL Insert Into Select ..................................................................................................................................11
SQL Create Database ...................................................................................................................................11
SQL Create Table .........................................................................................................................................11
SQL Constraints ...........................................................................................................................................12
SQL Not Null ...............................................................................................................................................12
SQL Unique .................................................................................................................................................13
SQL Primary Key.........................................................................................................................................13
SQL Foreign Key .........................................................................................................................................14
SQL Check ...................................................................................................................................................14
SQL Default .................................................................................................................................................14
SQL Create Index .........................................................................................................................................15
SQL Drop .....................................................................................................................................................15
SQL Alter .....................................................................................................................................................15
SQL

Page 1

SQL Null ......................................................................................................................................................16
SQL General Data Types .............................................................................................................................17
References ....................................................................................................................................................18

SQL

Page 2

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

What Can SQL do?
 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

What is RDBMS?
 RDBMS stands for Relational Database Management System.
 RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server,
IBM DB2, Oracle, MySQL, and Microsoft Access.
 The data in RDBMS is stored in database objects called tables.
 A table is a collection of related data entries and it consists of columns and rows.

SQL

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SQL Select
Definition

The SELECT statement is used to select data from a database.
The result is stored in a result table, called the result-set.

Syntax

SELECT column_name
FROM table_name;

Example

SELECT City FROM Customers;

SQL Select Distinct
Definition

The SELECT DISTINCT statement is used to return only distinct
(different) values.

Syntax

SELECT DISTINCT column_name,column_name
FROM table_name;

Example

SELECT DISTINCT City FROM Customers;

SQL Where
Definition

The WHERE clause is used to filter records.

Syntax

SELECT column_name, column_name
FROM table_name
WHERE column_name operator value;

Example

SELECT * FROM Customers
WHERE Country='Mexico';

SQL

Page 4

SQL And & Or
The AND operator displays a record if both the first condition AND the
Definition

second condition are true.
The OR operator displays a record if either the first condition OR the
second condition is true.

Syntax

SELECT column_name, FROM table_name
WHERE column_name (AND/OR) column_name;

Example

WHERE Country='Germany' AND City='Berlin';

SQL Order By
Definition
Syntax
Example

The ORDER BY keyword is used to sort the result-set by one or more
columns.
SELECT column_name, column_name
FROM table_name
ORDER BY column_name, column_name ASC|DESC;
ORDER BY Country DESC;

SQL Insert Into
Definition

Syntax

Example

SQL

The INSERT INTO statement is used to insert new records in a table.
INSERT INTO table_name
VALUES (value1, value2, value3,...);
INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...);
INSERT INTO Customers (CustomerName, City, Country)
VALUES ('Cardinal', 'Stavanger', 'Norway');

Page 5

SQL Update
Definition
Syntax
Example

The UPDATE statement is used to update existing records in a table.
UPDATE table_name
SET column1=value1, column2=value2,...
WHERE some_column=some_value;
UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg'
WHERE CustomerName='Alfreds Futterkiste';

SQL Delete
Definition

The DELETE statement is used to delete rows in a table.

Syntax

DELETE FROM table_name
WHERE some_column=some_value;

Example

DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND
ContactName='Maria Anders';

SQL Select Top
Definition
Syntax
Example

SQL

The SELECT TOP clause is used to specify the number of records to
return.
SELECT TOP number|percent column_name(s)
FROM table_name;
SELECT TOP 2 * FROM Customers;
SELECT TOP 50 PERCENT * FROM Customers;

Page 6

SQL Select Top
Definition
Syntax
Example

The SELECT TOP clause is used to specify the number of records to
return.
SELECT TOP number|percent column_name(s)
FROM table_name;
SELECT TOP 2 * FROM Customers;
SELECT TOP 50 PERCENT * FROM Customers;

SQL Like
Definition

The LIKE operator is used to search for a specified pattern in a column.

Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;

Example

WHERE City LIKE 's%';

SQL Wildcards
Definition

Wildcard characters are used with the SQL LIKE operator. They are used

Syntax

to search for data within a table.
FROM table_name
WHERE column_name LIKE pattern;
WHERE City LIKE 'ber%';

Example

WHERE City LIKE '_erlin';
WHERE City LIKE '[!bsp]%';

SQL

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SQL IN
Definition

The IN operator allows you to specify multiple values in a WHERE clause.

Syntax

FROM table_name
WHERE column_name IN (value1,value2,...);

Example

WHERE City IN ('Paris','London');

SQL Between
Definition

The BETWEEN operator selects values within a range. The values can be

Syntax

numbers, text, or dates.
FROM table_name
WHERE column_name BETWEEN value1 AND value2;
SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20;

Example

SELECT * FROM Products
WHERE Price NOT BETWEEN 10 AND 20;
SELECT * FROM Orders
WHERE OrderDate BETWEEN #07/04/1996# AND #07/09/1996#;

SQL Join
Definition

Syntax

Example

SQL

An SQL JOIN clause is used to combine rows from two or more tables,
based on a common field between them.
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;
SELECT Orders.OrderID, Customers.CustomerName,
Orders.OrderDate
FROM Orders
JOIN Customers
ON Orders.CustomerID=Customers.CustomerID;

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SQL Inner Join
The INNER JOIN keyword selects all rows from both tables as long as
Definition

Syntax

Example

there is a match between the columns in both tables. INNER JOIN is
the same as JOIN.
FROM table1
JOIN table2
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;

SQL Left Join
The LEFT JOIN keyword returns all rows from the left table (table1),
Definition

Syntax

Example

with the matching rows in the right table (table2). The result is NULL
in the right side when there is no match.
FROM table1
LEFT JOIN table2
FROM Customers
LEFT JOIN Orders

SQL Right Join
The RIGHT JOIN keyword returns all rows from the right table
Definition

Syntax

Example

SQL

(table2), with the matching rows in the left table (table1). The result
is NULL in the left side when there is no match.
FROM table1
RIGHT JOIN table2
SELECT Orders.OrderID, Employees.FirstName
FROM Orders
RIGHT JOIN Employees
ON Orders.EmployeeID=Employees.EmployeeID
ORDER BY Orders.OrderID;

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SQL Full Join
Definition

Syntax

Example

The FULL OUTER JOIN keyword returns all rows from the left table
(table1) and from the right table (table2).
FROM table1
FULL OUTER JOIN table2
FROM Customers
FULL OUTER JOIN Orders

SQL Union
Definition
Syntax

Example

The SQL UNION operator combines the result of two or more SELECT
statements.
SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;
SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;

SQL Select Into
Definition
Syntax
Example

SQL

The SELECT INTO statement selects data from one table and inserts it
into a new table.
SELECT *
INTO newtable [IN externaldb]
FROM table1;
SELECT *
INTO CustomersBackup2013
FROM Customers;

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SQL Insert Into Select
Definition

Syntax

Example

The INSERT INTO SELECT statement copies data from one table and
inserts it into an existing table.
INSERT INTO table2
SELECT * FROM table1;
INSERT INTO table2
(column_name(s))
FROM table1;
INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers;
INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers
WHERE Country='Germany';

SQL Create Database
Definition

The CREATE DATABASE statement is used to create a database.

Syntax

CREATE DATABASE dbname;

Example

CREATE DATABASE my_db;

SQL Create Table
The CREATE TABLE statement is used to create a table in a database.
Definition

Syntax

SQL

Tables are organized into rows and columns; and each table must have a
name.
CREATE TABLE table_name
(
column_name1 data_type(size),
....
);

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Example

CREATE TABLE Persons
(
PersonID int,
LastName varchar(255),
FirstName varchar(255),
Address varchar(255),
City varchar(255)
);

SQL Constraints
Definition

Syntax

Example

SQL constraints are used to specify rules for the data in a table.
CREATE TABLE table_name
(
column_name1 data_type(size) constraint_name,
....
);
NOT NULL- Indicates that a column cannot store NULL value.
UNIQUE- Ensures that each row for a column must have a unique
value.
PRIMARY KEY- A combination of a NOT NULL and UNIQUE. Ensures
that a column (or combination of two or more columns) have an
unique identity which helps to find a particular record in a
table more easily and quickly.
FOREIGN KEY- Ensure the referential integrity of the data in
one table to match values in another table
CHECK- Ensures that the value in a column meets a specific
condition.
DEFAULT- Specifies a default value when specified none for
this column.

SQL Not Null
Definition

Example

SQL

The NOT NULL constraint enforces a column to NOT accept NULL
values.
CREATE TABLE Persons NotNull
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
City varchar(255)
)

Page 12

SQL Unique
Definition

Example

The UNIQUE constraint uniquely identifies each record in a database
table.
CREATE TABLE Persons Unique
(
P_Id int NOT NULL,
City varchar(255),
UNIQUE (P_Id)
)

SQL Primary Key
The PRIMARY KEY constraint uniquely identifies each record in a
database table.

Definition

Primary keys must contain unique values.
A primary key column cannot contain NULL values.
Each table should have a primary key, and each table can have only ONE

Example

SQL

primary key.
(
P_Id int NOT NULL,
City varchar(255),
PRIMARY KEY (P_Id)
)

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SQL Foreign Key
Definition

Example

A FOREIGN KEY in one table points to a PRIMARY KEY in another
table.
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(P_Id)
)

SQL Check
Definition

Example

The CHECK constraint is used to limit the value range that can be
placed in a column.
(
P_Id int NOT NULL,
City varchar(255),
CHECK (P_Id>0)
)

SQL Default
The DEFAULT constraint is used to insert a default value into a column.
Definition

Example

SQL

The default value will be added to all new records, if no other value is
specified.
(
P_Id int NOT NULL,
City varchar(255),
CHECK (P_Id>0)
)

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SQL Create Index
The CREATE INDEX statement is used to create indexes in tables.
Definition

Indexes allow the database application to find data fast; without reading
the whole table.

Syntax

CREATE INDEX index_name
ON table_name (column_name)

Example

CREATE INDEX PIndex
ON Persons (LastName)

SQL Drop
The DROP statement is used to delete a table or database.
Definition

Syntax
Example

TRANCATE statement is when we only want to delete the data inside
the table, and not the table itself.
DROP TABLE table_name
DROP DATABASE database_name
TRUNCATE TABLE table_name
DROP TABLE Person
DROP DATABASE test
Truncate TABLE Person

SQL Alter
Definition

The ALTER TABLE statement is used to add, delete, or modify columns

Syntax

ALTER TABLE table_name
ADD column_name datatype

Example

ALTER TABLE Persons
DROP COLUMN DateOfBirth

SQL

in an existing table.

Page 15

SQL Null
NULL values represent missing unknown data.
Definition

By default, a table column can hold NULL values.
Note: It is not possible to compare NULL and 0; they are not

Syntax

Example

SQL

equivalent.
SELECT column_name FROM table
WHERE column_name IS NULL
SELECT column_name FROM table
WHERE column_name IS NOT NULL
SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NULL
SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NOT NULL

Page 16

SQL General Data Types
Database Type

Description

CHARACTER(n)

Character string. Fixed-length n

VARCHAR(n) or
CHARACTER VARYING(n)
BINARY(n)

Character string. Variable length. Maximum
length n
Binary string. Fixed-length n

BOOLEAN

Stores TRUE or FALSE values

VARBINARY(n) or
BINARY VARYING(n)
INTEGER(p)

Binary string. Variable length. Maximum length
n
Integer numerical (no decimal). Precision p

SMALLINT

Integer numerical (no decimal). Precision 5

INTEGER


BIGINT


DECIMAL(p,s)

REAL

Exact numerical, precision p, scale s. Example:
decimal(5,2) is a number that has 3 digits
before the decimal and 2 digits after the
decimal
Exact numerical, precision p, scale s. (Same as
DECIMAL)
Approximate numerical, mantissa precision p. A
floating number in base 10 exponential
notation. The size argument for this type
consists of a single number specifying the
minimum precision
Approximate numerical, mantissa precision 7

FLOAT


DOUBLE PRECISION


DATE

Stores year, month, and day values

TIME

Stores hour, minute, and second values

TIMESTAMP

Stores year, month, day, hour, minute, and
second values
Composed of a number of integer fields,
representing a period of time, depending on the
type of interval
A set-length and ordered collection of elements

NUMERIC(p,s)
FLOAT(p)

INTERVAL
ARRAY
MULTISET
XML

SQL

A variable-length and unordered collection of
elements
Stores XML data

Page 17

References
http://www.w3schools.com/sql/

SQL

Page 18

Sql

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