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database:is acollection of system trhat has a collection of data .
relatiobnal database store data easily retriveed ,managed,and update.

What is sql:
Sql:-structued query language.
sql is the language to communicate with databsees.


4 types of sql command
1): data Defination language:
  create,alter,Drop truncate

2. DML: data manipulation language:
  select.insert, update, delete

3. Data control langauge DCL:-
     grant, revoke

4 trasaction control language (tcl):
  commit, rollback

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sql application
CURD

create update read delete

--------------------------------------------------------------------------------
difference between sql and nosql

sql-relational database, data store in the table , 
    sql databace have fixed or static or predefine schema
    low performance with huge volume of data
    mysql,db2,oracle,sql-server

nosql -nonrelational databse, data store in key:value pair, document, graph databse,
   nosql have dynamic schema,  Easily work with huge volume of data
   mongodb


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Datatype:
string: char, varchar
Numeric :int,float, 
bool :True and false
date& time :date ,datetime

---------------------------------------------------------------
Contraints:
contraints are used to specify rules for data in the table.
this ensure the accuracy and relibility  of the data in the table.

syntax:
    create table table_name(
      col1 datatype contraints
      -----
)


Commonly used contraints

1:-Not Null:-Ensure that the column cannot have null value.
2:Unique :-ensure that all values in a column are different.
3.Default:-set a default value for column if no value is specified.
4.primary key:-combination of not null and unique
5.foreign key :-a foreign key is a column used to link between two more tables together.
      a table have any number of forein key ,can contain duplicate and null values

6.check :- ensure thet the value in a column satisfies a specific condition



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DBMS provide various level abstraction
1.pysical level :it is the lowest level of abtraction which describe how the data is actully stored

2.logical level: it is the next higher level of abtraction that describe what data is stored in the database 
whet relationaship exists between varies data element in the database

3.view level: It is use to simplify the user interaction with the system   

-------------------------------------------------------------
Normalization:
it is a database  design technique that organize table in a manner that reduce redudency and dependancy of data
- to avoid insertion ,deletion, updation anomaly

#1Nf, 2NF,3NF ,BCNF,

First normal form 1NF
-an column of atable cannot hold multiple value
-it should hold only automic value.
-each records needs to be unique


2NF
-it should be in the 1nf
-


  
create database first;
show databases;
use first;
create table Employee(
empid int,
name varchar(30),
address varchar(255),
salary int
);

insert into Employee values(104,"radha","nashik",67890);
insert into Employee values(105,"sita","satara",34567);
insert into Employee values(106,"anita","nagpur",234567);
select distinct * from Employee;

select * from Employee where address="pune";
select * from Employee where salary  between 10000 and 20000;
select * from Employee where address like "%ne";
select * from Employee where address like "ne%";
select * from Employee where address like "__ne";
select * from Employee  where address like "%gp%";

select * from Employee where address in("Nagpur","pune");
select * from Employee ;
select * from Employee order by salary asc;
select * from Employee order by salary desc;
select * from Employee where salary>50000  order by salary desc;
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