SQL-Primary key and foreign key Relation/Parent-child relationship between tables/ On delete cascade/foreign key constraint with Example

SQL-Primary key and foreign key Relation/Parent-child relationship between tables/ On delete cascade/foreign key constraint with Example

Suppose we have two table customer and supplier
CREATE TABLE supplier
( supplier_id numeric(10) not null,
 supplier_name varchar2(50) not null,
 contact_name varchar2(50),
 CONSTRAINT supplier_pk PRIMARY KEY (supplier_id)
);

insert into supplier values(1,'Sarat','Chand');
insert into supplier values(2,'Sartaj','Ahmed');
insert into supplier values(3,'Saral','Chand');


CREATE TABLE products
( product_id numeric(10) not null,
 supplier_id numeric(10) not null,
 CONSTRAINT fk_supplier
   FOREIGN KEY (supplier_id)
  REFERENCES supplier(supplier_id)
  ON DELETE CASCADE
);

insert into products values(101,1);
insert into products values(102,2);
insert into products values(103,3);

--Check/verify the entered data into the table using below command

select * from products;
select * from supplier ;

--not Allowed to add the product into the supplier table because the supplier id is not exist in the parent table name supplier

insert into products values(103,4);

--Error Message
--ORA-02291: integrity constraint (HR.FK_SUPPLIER) violated - parent key not found

So we can say that the table relation between table is established

--The data can be deleted from the supplier table because it is parent table but cannot delete the data into child table
--delete the data from supplier table whose supplier_id is 1;
delete from supplier where supplier_id=1;

delete from products where supplier_id=1;
--check the constraints
select * from user_cons_columns;
select * from user_constraints;

Program1- Write a program to print the Hello Message to the terminal

Solution-often we start writing the first program as hello Message.


So let us write the first hello program using various methods.

Method-1:Using Anonymous block 
Code-
SQL> begin
  2  dbms_output.put_line('HELLO');
  3  end;
  4  /
HELLO
PL/SQL procedure successfully completed.
SQL>

Method-2:Using PROCEDURE 
code-
SQL> SET SERVEROUTPUT ON
SQL> CREATE OR REPLACE PROCEDURE hello
  2  AS
  3  BEGIN
  4     dbms_output.put_line('Hello World!');
  5  END;
  6  /

Procedure created.

SQL>

Note- we can execute the procedure in two way -
Use SET SERVEROUTPUT ON  command to view the output on terminal-
1.
SQL> EXECUTE hello;
Hello World!

PL/SQL procedure successfully completed.
SQL>

2.
SQL> BEGIN
  2    hello;
  3  END;
  4  /
Hello World!

PL/SQL procedure successfully completed.
SQL>

Oracle-Concatenation Operator(||)

Concatenation Operator(||)

Concatenation operator is used to concatenate the column or string to another column or string and it is represented by two vertical bar (||).

SQL Statement-

select 'The employee Name '||Ename||' and employee id is '||empno As   "Employee Information" from emp

Result-
             Employee Information
The employee Name KING and employee id is 7839
The employee Name BLAKE and employee id is 7698
The employee Name CLARK and employee id is 7782
The employee Name JONES and employee id is 7566
The employee Name SCOTT and employee id is 7788
The employee Name FORD and employee id is 7902
The employee Name SMITH and employee id is 7369

Arithmatic Expression in MySQL-Addition,subtraction Multiplication and modulo operator

Arithmatic Expression in MySQL

Arithmatic Expression are the combination of arithmatic operator,constant numeric value and column name  in the SQL statements.
A list of arithmatic opertors are given below -
1.Addition(+)
2.Subtraction(-)
3.Multiplication(*)
4.Division(/)
5.Remainder or Modulo operator(%)

Note-
1.You can use arithmatic operator in any clause in SQL statement except FROM cluase.
2.The operator priority list is given below-
  * / + and -
 Priority Rule -Multiplication and division take the priority over Addition and Division.operators of same priority can be evaluated from left to right.
Parentheses are used to define the priority explicitly to remove the ambiguity.

Example: SQL Arithmetic Operators
1.SELECT 150+10-5*5/5;

Result:
Number of Records: 1
150+10-5*5/5
155

=======

Suppose we have the empsal table with five record and its details are given below-
Create table empsal ( id nuber , name varchar2(30),salary number(8,2));
insert into empsal(id,name, salary) values(1,'Ajay', 10000);
insert into empsal (id,name, salary) values(2,'Amit', 11000);
insert into empsal (id,name, salary) values(3,'Ashok', 7000);
insert into empsal (id,name, salary) values(4,'Aarif', 6000);
insert into empsal (id,name, salary) values(5,'Vinod', 5000);
2. verify the record
Result:
Number of Records: 5
id name salary
1 Ajay 10000
2 Amit 11000
3 Ashok 7000
4 Aarif 6000
5 Vinod 5000

SQL plus (+) operator:It is used to add two or more numbers/expressions
Example-
1.For Number computation
SELECT 150+10;

2.Write a query to find the the increment of the salary of employee by Rs 300.
SELECT Id, name , salary+300 as " Salary" from empsal;
Result:
Number of Records: 5
id name Salary
1 Ajay 10300
2 Amit 11300
3 Ashok 7300
4 Aarif 6300
5 Vinod 5300

2.SQL minus (-) operator -subtract one expression /number from another expression /number.

Example-
1.select 150-5;

Number of Records: 1
150-5
145

2.Write a query to display the Ashok monthly salary after PF deduction of Rs 1500.
 SELECT name, salary-1500 "Ashok In hand Salary" FROM empsal where id=3;

Result:
Number of Records: 1
name Ashok In hand Salary
Ashok 5500

3.SQL multiply ( * ) operator  used to multiply two or more expressions or numbers.

Example-

1.Display the Ashok's Annual salary.
SELECT Id, name , salary as "Monthly Salary", 12*salary as "Yearly Salary" from empsal

Result:
Number of Records: 1
id name Monthly Salary Yearly Salary
3 Ashok 7000         84000

4.SQL divide ( / ) operator-divide one expressions /numbers by another.
1.Write a query to share the Ashok's Annual salary among his four friends equally.
SELECT Id, name ,(12*salary)/4 as "Ashok's friend share" from empsal where id=3

Result:
Number of Records: 1
id name Ashok's friend share
3 Ashok 21000

Sorting ASC,DESC-ORDER BY clause display the rows in ASC|DESC order for an expression,column position or an alias.

ORDER BY Clause-
The ORDER BY clause is used to sort the data in ascending(its default ) or 
descending order of one or more columns and use the key word ORDER BY.
ORDER BY clause display the rows in ASC|DESC order for an expression,column position or an alias. 

Syntax-

SELECT   *|[DISTINCT]Column|expression [Alias]
From Table_Name
[WHERE <Condition(s)>]
[ORDER BY Column|Expression [ASC|DESC]];

SELECT -a list of columns
* -Select the all columns 
DISTINCT-suppresses the duplicates 
alias-alternate name of the colunm(s) that is/are used as the heading of that column(s).  
Table_name-specifies the table name containing the column(s). 
WHERE<Condition(s)>- the condition must meet to retrieve the data from the database.
ORDER BY Column|Expression -order the rows in Acending or descending order 

Example- 

1.Write the query to find employee information order by name.

Query-    SELECT * FROM employee order by name;
Output-
Number of Records: 5
ID Name email          address phone_number salary
2 Ajay ajay@gmail.com Hyderbad 16756890 51000
4 Aman Aman@gmail.com Lucknow         26756890 51000
3 Amit amit@gmail.com Delhi         16756890 51000
5 Hari Hari@gmail.com Lucknow         36756890 15000
1 sharat sarat@gmail.com Hyderbad 123456890 5000

2.Write the query to selects all employees from the "employee" table, sorted by the "Name" and the "Salary" column.

Query- SELECT * FROM employee order by name, salary;
Output-
Number of Records: 5
ID Name email          address phone_number salary
2 Ajay ajay@gmail.com Hyderbad 16756890 51000
4 Aman Aman@gmail.com Lucknow         26756890 51000
3 Amit amit@gmail.com Delhi         16756890 51000
5 Hari Hari@gmail.com Lucknow          36756890 15000
1 sharat sarat@gmail.com Hyderbad 123456890 5000

3.Display the name and the salary of the employees from the "employee" table, sorted ascending by the name and descending by the salary. 

Query- SELECT name,salary FROM employee order by name, salary DESC;
Output-
Number of Records: 5
Name salary
Ajay 51000
Aman 51000
Amit 51000
Hari 15000
sharat 5000

4.Display the name and the yearly salary of the employees from the employee table and sort by Annual_salary in ascending. 

Query-SELECT Name , salary*12  Annual_salary FROM employee  order by Annual_salary;
 Alternate -SELECT Name , salary*12  Annual_salary FROM employee  order by 2;
Output-
Number of Records: 5
Name Annual_salary
sharat 60000
Hari 180000
Ajay 612000
Amit 612000
Aman 612000

5.Display the name as Employee Name  and the yearly salary  as Annual_salary of the employees from the employee table and 
sorted descending order by the Annual_salary

Query-SELECT Name "Employee Name", salary*12  Annual_salary FROM employee  order by 2 DESC;
Output-
Number of Records: 5
Employee Name Annual_salary
Ajay           612000
Amit           612000
Aman           612000
Hari           180000
sharat           60000

WHERE Clause-To limit the retrieval of the data from the database for given condition

WHERE Clause
Where clause is used to limit the retrieval of the data from the database for given condition 
and use the key word WHERE.Where clause follows the FROM clause in the SQL Statement.

Syntax-

SELECT   *|[DISTINCT]Column|expression [Alias]
From Table_Name;
[WHERE <Condition(s)>]

SELECT -a list of columns
* -Select the all columns 
DISTINCT-suppresses the duplicates 
alias-alternate name of the column(s) that is/are used as the heading of that column(s).  
Table_name-specifies the table name containing the column(s). 
WHERE<Condition(s)>- the condition must meet to retrieve the data from the database.

Note- Condition is combination of column names,constants,variables,expressions and comparison operator.

Example- 

1.Write the query to find the id,name,address of employee whose address is Lucknow.

Query-    select ID,Name,Address from employee where address='Lucknow';
Output-
Number of Records: 2
ID   Name  address
4    Aman  Lucknow
5    Hari  Lucknow

2.Write the query to retrieve employees details whose salary is more than 10000 and less than 50000. 

Query-  SELECT * FROM employee where salary>10000 and salary<50000
Output-
Number of Records: 1
ID  Name      email             address  phone_number   salary
5   Hari   Hari@gmail.com        Lucknow   36756890      15000

3.Write the query to display the id,name and the yearly salary of the employees whose annual salaries are less than 200000.

Query-SELECT ID , Name , salary*12  Annual_salary FROM employee where Annual_salary<200000;
Output-
Number of Records: 2
ID Name     Annual_salary
1 sharat    60000
5 Hari      180000

4.Write the query to display the id,name and the yearly salary of the employees and also label the column heading id as Emp_Id,name as Employee Name and salary as 
Yearly Salary Package.

Query-  SELECT ID as Emp_Id, Name as "Employee Name", salary*12 as "Yearly Salary Package" FROM employee;
Output-
Number of Records: 5
Emp_Id Employee Name     Yearly Salary Package
1         sharat         60000
2         Ajay           612000
3         Amit           612000
4         Aman           612000
5         Hari           180000

SELECT Statement-To retrieve the data from the database

SELECT Statement

Select statement is used to retrieve the data from the database.We use the key word SELECT.

Using the Select statement, we can choose the column(s)of the same table or different tables using the join and 

also can select the number of the rows either same or different tables.

Syntax-

SELECT   *|[DISTINCT]Column|expression [Alias]
From Table_Name;

SELECT -a list of columns
* -Select the all columns 
DISTINCT-suppresses the duplicates 
alias-alternate name of the column(s) that is/are used as the heading of that column(s).  
Table_name-specifies the table names containing the column(s). 

Example- 

1.Write the query to select the all columns of the table employee.
Query-    select * from employee;
Output-
Number of Records: 5
ID Name email                 address       phone_number salary
1 sharat sarat@gmail.com          Hyderabad 123456890 5000
2 Ajay ajay@gmail.com          Hyderabad 16756890 51000
3 Amit amit@gmail.com          Delhi         16756890 51000
4 Aman Aman@gmail.com          Lucknow 26756890 51000
5 Hari Hari@gmail.com          Lucknow 36756890 15000

2.Write the query to find the distinct address in the employee table. 
Query-  SELECT distinct address FROM employee
Output-
Number of Records: 3
address
Hyderabad
Delhi
Lucknow

3.Write the query to display the id,name and the yearly salary of the employees and also 

label the column heading id as Employee_Id,name as Name and salary as Annual Salary.
Query-  SELECT ID as Employee_Id, Name as "Name", salary*12 as "Annual salary" FROM employee;
Output-
Number of Records: 5
Employee_Id Name Annual salary
1         sharat 60000
2         Ajay 612000
3         Amit 612000
4         Aman 612000
5         Hari 180000

4.Write the query to display the id,name and the yearly salary of the employees  whose annual salaries are greater 200000 and also 

label the column heading id as Employee_Id,name as Name and salary as Annual_Salary.
Query-SELECT ID as Employee_Id, Name as "Name", salary*12  Annual_salary FROM employee where Annual_salary>200000;
Output-
Number of Records: 3
Employee_Id Name Annual_salary
2        Ajay 612000
3        Amit 612000
4        Aman 612000