DATABASES AND SQL

Introduction Relation: Relation means table(data is arranged in rows and columns) Domain : A domain is a pool of values appearing in given column. Eg:

Tuple : The rows of a relation Attribute : The columns of a relation. Attributes Tuple

Degree : Number of attributes(columns) Cardinality: Number of tuples(rows) Degree 2 Cardinality 4

Key Primary Key: Set of one of one more attribute that can uniquely identify tuples within a relation Candidate key: is one or more column in table that uniquely identify each row in a table (can act as primary key). Alternate Key: candidate key is not a primary key

Data types SQL data types are classified into three Numeric String Date

1. Numeric data type: - Length of numeric data type Range decimal places ( 0 to 30) - decimal must be 2 less than length - 2 categories of integer data types are integer(whole numbers) data type TINYINT, SMALLINT, MEDIUMINT, INT, INTEGER, BIGINT Floating point data types are FLOAT,DOUBLE, DOUBLEPRECISION, REAL, DECIMAL, DEC, NUMERIC, FIXED

2. String data types - used to store various types of data - four categories of string data types are CHARACTER, BINARY, TEXT and LIST commonly used data type is character character is classified in two Char uses n byte storage (blank spaced filled with space) varchar uses less storage space

3. Date & Time -yyyy –mm-dd format categories of date & time data types DATE, TIME, DATETIME,YEAR, TIMESTAMP

SQL Statements Sql is made up of set of statements that define the structure of database, store and manage data within that structure and control access to data. Sql statements are mainly divided in to three categories DDL(Data Definition Language) DML(Data Manipulation Language) DCL(Data Control Language)

DDL -( Data Definition Language ) DDL statements create, alter and delete data structure within table. DDL statements defines the type.Eg: create, alter, Drop DML – (Data Manipulation Language ) DML is concerned with data stored in a table. Eg: Insert, update, delete and select. DCL – (Data Control Language) DCL statements controlling the access to database. Eg: grant and revoke.

CREATE TABLE command Create table ( [ ][NOT NULL|NULL][DEFAULT ] [PRIMARY KEY( ],[CHECK EXPRESSION][UNIQUE],..)

Example create table student ( rollno int primary key,column level definition name char (10) );

Create a table student using following information create table student ( Rollno int(4) Primary key, Name varchar(10) Total int(2)); you can’t define a primary key on multiple columns at the column level Column nameData typeSizeconstrain RollnoInt4Primary key NameVarchar10 TotalInt2

INSERT Command To insert row in table Syntax 1 : INSERT INTO (,..) VALUES (,..); Eg: Insert into student (rollno, name,total) values (12101,’arun’,400); if column name are included value clause must include a value for each column

Format 2 INSERT INTO VALUES (,..), Insert into student values (12101,’arun’,400), values(12102,’anil’, 500);

INSERT INTO VALUES (,..), (,..), Eg: Insert into student values (12101,’arun’,400), (12102,’anil’, 500), (12103,’amit’,550), (12104,neem,450);

*Points to remember inserting number : inserting char : inserting date :<’yyyy-mm-dd’) inserting null : NULL  if column name are not included you must provide value for every column in table

UPDATE Command To modify the existing row content UPDATE SET [where ]; where clause determines the which row in a table are updated. Eg : Update student set total =450 where rollno=12101;

DELETE Command To remove row /data from a table DELETE FROM [where expression]; Eg : delete from student where roll = 12102;

SELECT Command To retrieve data from MySql tables we can use SELECT statement SELECT {ALL | DISTINCT } {* | | [AS] } FROM { }{,[ ]}{…….} [WHERE ] [GROUP BY ] [HAVING ] [ORDER BY ]

Select command let you to make queries on the database Form1: To retrive columns Select [, colum name, colum name …] from ; Eg : select rollno, name from student; Form 2: if you want to see the entire table. The (*) can be substituted. Select * from Eg: Select * from student;

Select with - DISTINCT clause or ALL To eliminate duplicates rows from result of a SELECT statement. Form 3 Select DISTINCT column name from Eg: Select distinct name from student; Form 4 Select ALL column name from Eg: Select ALL name from student;

Retrieving specific rows – where clause Select [, colum name, colum name …] from where ; Eg: select * from student where rollno=12101; Relational operators: (Greater than), =(greater than or equal), =(Equal),!= or <>(Not equal). Logical operator : and, or not

Between clause – to set range Select [, colum name, colum name …] from [where column name between value1 and value 2 ; The above statement means Select [, colum name, colum name …] from [where column name>= value1 and column name <= value 2 ; Eg: select * from student where total between 400 and 500. select * from student where total >= 400 and total<= 500.

IN clause – to select values Select [, colum name, colum name …] from [where column name IN( value1,value 2) ; The above statement means Select [, colum name, colum name …] from [where column name= value1 or column name < value 2 ; Eg: select * from student where total IN(400, 500). select * from student where total = 400 or total = 500.

Order by clause – for Sorting - Arrange rows in either ascending / descending order Select [, colum name, colum name …] from [where order by [asc/desc]] Default sorting ascending order(asc) Eg: select * from student where total >= 400 and total<= 500 order by name.

Group by – for grouping similar records Select [, column name, column name …] from [ group by having ] If you are using group by clause and you want to restrict rows use having clause instead of where. Eg: select * from student where group by total having total >= 400 and total<= 500.

Group functions MAX() -> Returns Maximum value from a given column MIN() -> Returns Maximum value from a given column AVG() -> Returns Average value from a given column SUM()-> Returns Sum of values in a given column COUNT() -> count number of rows (Excluding NULL) : COUNT(*) -> returns number of rows( including null)

Group function - Example Select Sum(Total) from student; Select Max(Total) from student; Select Min(Total) from student; Select Avg(Total) from student; Select count() from student; Select Count(*) from student;

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