3-Data Manipulation Using SQL-Part1

8/2/2019 3-Data Manipulation Using SQL-Part1

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Introduction To SQL


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lSQL uses English keywords & user-defined names

By convention, keywords are upper-caseText data is enclosed using single quotes ( ' )Round brackets (() are used to group related itemsCommas (,) separate items in a list Statements areterminated with a semicolon (;)

CREATE TABLE Staff (

StaffNo INTEGER,

Salary FLOAT,

Lname CHAR(20)

);

INSERT INTO Staff VALUES (32, 25000.0, 'Smith');

SQL Syntax


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Some SQL Key words

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

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


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Creating a Database

SyntaxCREATE DATABASE database_name

ExampleCREATE DATABASE my_db


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Creating a Table

Syntax

CREATE TABLE table_name(column_name1 data_type,column_name2 data_type,column_name3 data_type,....)


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Create Table Example


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Some SQL Data Types

Data Type Syntax ExplanationInteger int

decimal decimal(p,s)Where p is a precisionvalue; s is a scale value

float float(p)

Where p is a precision

value.

Character char(x)

Where x is the number ofcharacters to store. This datatype is space padded to fillthe number of charactersspecified.

Character varying Varchar(x)Where x is the number ofcharacters to be stored

date dateStores year, month, andday values.

time timeStores the hour, minute,and second values.C


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SQL Constraints

Constraints are used to limit the type of data that can go into atable.

Constraints can be specified when a table is created (with the

CREATE TABLE statement) or after the table is created (with theALTER TABLE statement).

We will focus on the following constraints:NOT NULL

UNIQUEPRIMARY KEYFOREIGN KEYCHECKDEFAULT


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SQL Constraints Primary Key

Primary Keyis a set of attributes which identifies uniquely atuple (i.e., a row in a table) E.g., your NRIC or your email address The combination (name, city) in the branch table

You cannot have two tuples with the same Primary Key in a table E.g., there cannot be two persons with the same NRIC. Therecannot be two branches with the same name in the same city


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SQL Constraints Primary Key etc

Eg 1:CREATE TABLE branch( name varchar(10),

city varchar(20),

director varchar(20),assets number,PRIMARY KEY (name, city));


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SQL Constraints Primary Key etc

Eg 2:CREATE TABLE Persons(P_Id int PRIMARY KEY,LastName varchar(255) NOT NULL,

FirstName varchar(255),Address varchar(255),City varchar(255));


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SQL Constraints - UNIQUE

The UNIQUE constraint uniquely identifies each record in a databasetable.

The UNIQUE and PRIMARY KEY constraints both provide a guaranteefor uniqueness for a column or set of columns.

A PRIMARY KEY constraint automatically has a UNIQUE constraintdefined on it.


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SQL Constraints UNIQUE etc

The following SQL creates a UNIQUE constraint on the "P_Id"column when the "Persons" table is created:

CREATE TABLE Persons(

P_Id int PRIMARY KEY,NIC int,LastName varchar(255),FirstName varchar(255),Address varchar(255),

City varchar(255),UNIQUE (NIC))


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SQL Constraints NOT NULL

The NOT NULL constraint enforces a column to NOT accept NULLvalues

The following SQL enforces the "P_Id" column and the "LastName"

column to not accept NULL values:

CREATE TABLE Persons(P_Id int PRIMARY KEY,LastName varchar(255) NOT NULL,

FirstName varchar(255),Address varchar(255),City varchar(255));


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SQL Constraints - Check

The CHECK constraint is used to limit the value range that can beplaced in a column.

If you define a CHECK constraint on a single column it allows only

certain values for this column.

If you define a CHECK constraint on a table it can limit the valuesin certain columns based on values in other columns in the row.


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SQL Constraints Check

The following SQL creates a CHECK constraint on the "P_Id"column when the "Persons" table is created. The CHECK constraintspecifies that the column "P_Id" must only include integersbetween 0 and 1000.

CREATE TABLE Persons(P_Id int PRIMARY KEY,LastName varchar(255) NOT NULL,FirstName varchar(255),

Address varchar(255),City varchar(255),CHECK (P_Id BETWEEN 0 AND 1000));


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SQL Constraints Foreign Key

A FOREIGN KEY in one table points to a PRIMARY KEY in another table.

Example

Foreign Key

Primary Key


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SQL Constraints Foreign Key

A FOREIGN KEY in one table points to a PRIMARY KEY in another table.

Example :

CREATE TABLE Orders(O_Id int,OrderNo int NOT NULL,P_Id int,PRIMARY KEY (O_Id),

FOREIGN KEY (P_Id) REFERENCES Persons(P_Id))


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SQL Select

SyntaxSELECT column_name(s)FROM table_name

ExampleSELECT LastName,FirstName FROM Persons


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SQL Select Example


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SELECT DISTINCT

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name(s)

FROM table_name


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SELECT DISTINCT - Example


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SQL WHERE Clause

SQL WHERE Syntax

SELECT column_name(s)

FROM table_name

WHERE column_name operator value


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SQL WHERE Example


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SQL AND OR Operators

The AND operator displays a record if boththe first condition and the second conditionis true.

The OR operator displays a record if eitherthe first condition or the second condition

is true.


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AND Operator Example


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OR Operator Example


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SQL WHERE Example Cont...

View the the names of the customers with respect to each order ?

Example

Foreign Key

Primary Key


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SQL WHERE Example cont...

Answer :

SELECT o.OrderNo, p.FirstName, p.LastName

From Orders o, Persons p

Where o.P_ID=p.P_ID


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SQL Order By Clause

ORDER By example

SELECT column_name(s)

FROM table_name

ORDER BY column_name(s) ASC|DESC


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SQL Order By Example


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SQL Group By Clause

SELECT column_name,aggregate_function(column_name)

FROM table_name

WHERE column_name operator value

GROUP BY column_name


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SQL Group By Clause

3-Data Manipulation Using SQL-Part1

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