Aggregate Functions and Group By Clause in Oracle with Examples #Diksha Oracle Training Centre

 Aggregate Functions and Group By Clause Oracle with Examples.

 

Hello Everyone,

Today I will  discuss about  Aggregate function in SQL by using Group By Clause and different clauses with some examples . Please go tjrough my previous blogs in Archive folder for classification of SQL, Commands and  SQL joins for your understanding.

 Aggregate Functions Allows us to perform a calculation on a set of values to return a single value . We can use Group by Clause to group the result-set by one or more columns. Also we can use Having clause to restrict or filter the data as per our requirement.

Note: Whenever we use Aggregate function in SQL we can’t able to use where condition. To restrict or filter the record we need to use having clause instead of Where.

Below is the most commonly used Aggregate function in SQL.

 

MAX : Max function  used to get the maximum values in a set of values.

COUNT : This function used to count rows in specified tables.

AVG   : This function is used to calculate the average of set values.

SUM  : This Function is used to calculate the sum of Values.

MIN : MIN Function  used to get the minimum values in a set of values.

Apart from that many Aggregate functions available in Oracle database like STDDEV,VARIANCE, RANK etc . But most commonly used aggregate functions are MAX, MIN, AVG,COUNT and SUM .

 

SQL Aggregate Functions Examples :

Let’s understand with some examples of using SQL aggregate functions:

Suppose I have one table Employee if i want to see the max sal of employees then we use below syntax:

SELECT MAX(SALARY)  AS MAXIMUM_SALARY

FROM EMPLOYEE;

Max function  used to get the maximum values in a set of values , but it will only give one values.

Above query will give only 1 result as we know function must return a value but only single value, suppose if I want to see the maximum salary of employee for each employee we can use Group by Clause to  get the Maximum Salary for each employee.

 

Below is the command for this to get maximum salary by  dept_no

select max(salary)

 as Maximum_salary,

 emp_id,

 empname

 from employee

 group by emp_id, empname;

 

Below is the  output of both query.

 

 

 

 

 

To filter or restrict the data in aggregate function we can use Having instead of where condition.

Let’s take one example: If I want to see the max salary greater than 40000 for each employee id , then we can use below SQL command:

 

select max(salary),

 emp_id,

 empname

 from employee

 group by emp_id,empname

 having max(salary) > 40000;

Below is the image output for your reference of above query.

 

 

Here we see the uses of group by and having clause uses in Aggregate Function.

We can use other Function in same Manner , let’s have use of SUM function and other functions you can use in the same way what I have written.

 Select Sum(salary) as sum_salary ,

empname

From employee ;

Below is the image output for your reference of above query.

Here we used function so it returns only 1 row that is sum value of salary.

 

If I want to get the sum of salary employee id wise then we can use below query by using group by clause:

select sum(salary) as sum_salary,

emp_name,

emp_id

 from employee

group by emp_name ,emp_id;

 

Below is  the  output  of above query.

 

 

If I want to restrict the data as I want to see the sum of salary is greater than 40000 below is the query we can use to restrict the data by having clause:

 

select sum(salary) ,

empname,

emp_id

 from employee

 group by empname,emp_id

having sum_salary >40000;

 

Below is the output of above query.

 

I have given examples of 2 aggregate functions with Group by and having clause. Please try to use different functions like MIN , COUNT,MAX, AVG , STDDEV VARIANCE etc in same way as per your requirement . Design and create table and put some logical data and do the analysis as per your need. You can follow my previous blogs for  creating  and inserting the data in tables by using DDL and DML .

 

You can use Functions  in Subquery , Joins and once I started PL/SQL blogs this functions can be very useful.

 

For now I just right one Sub query for your reference and please you can also try to write aggregate query using group by clause in different scenario.

 

Below is the Sub query :

select max(salary),

emp_id,

EMPNAME

 from employee

where emp_id in

 (select emp_id

 from department

  where DEPT_NAME='IT')

group by emp_id,EMPNAME

 

Below is the image output for your reference of above query.

Here we not use having clause because  as in Inner query we use simple select query to filter the data.

Note: Sub query Part I will cover in my next blog with more details   

For now I suggest you to design/Create 2 or 3 tables with logical data and use aggregate functions with group by having clause and write some meaningful queries as you can take reference of Join from my previous blogs.

 

Group by and Aggregate functions mostly used in companies to generate report and do some trend analysis.

 

 Please go through this blog Carefully and try to use all the aggregate functions and let me know if you any issues. This blog is important for fresher’s who is preparing for interview as SQL developer.

 

In next Blog I will come with Oracle sub queries and Co-related Sub queries.

 

Thanks