calculate average rating in sql server

Question

this is my table:

I want to fetch records of Those Vendor which contai

Answer 1

Use aggregate function AVG():

Try this:

SELECT u.id, u.ServiceDescription, u.Skills, u.fullname, u.email, AVG(ISNULL(rv.rating, 0)) averagerating
FROM UserDetails u 
INNER JOIN VendorInCategory v ON v.VendorId=u.Id 
INNER JOIN CategoryMaster c ON v.CategoryId=c.Id 
LEFT JOIN Review rv ON u.Id=rv.VendorId  
WHERE (u.ServiceDescription LIKE '%Plaster%' OR u.Skills LIKE '%Plaster%' OR 
       c.Name LIKE '%Plaster%')
GROUP BY u.id, u.ServiceDescription, u.Skills, u.fullname, u.email
ORDER BY averagerating DESC;

EDIT

Other solution to implement this:

SELECT u.id, u.ServiceDescription, u.Skills, u.fullname, u.email, 
       ISNULL(rv.averagerating, 0) averagerating
FROM UserDetails u 
INNER JOIN VendorInCategory v ON v.VendorId=u.Id 
INNER JOIN CategoryMaster c ON v.CategoryId=c.Id 
LEFT JOIN (SELECT rv.VendorId, AVG(rv.rating) averagerating FROM Review rv GROUP BY rv.VendorId) rv ON u.Id=rv.VendorId  
WHERE (u.ServiceDescription LIKE '%Plaster%' OR u.Skills LIKE '%Plaster%' OR 
       c.Name LIKE '%Plaster%')
ORDER BY ISNULL(rv.averagerating, 0) DESC;

Answer 2

Many users have used the AVERAGE function to calculate the average of a series of data. But what do you do when you have summary data instead of individual responses and need to calculate an average? (For example, counts of the number of people who selected each rating on a 5-point rating scale like the rating of a product.)

How to Calculate a Weighted Average

Let’s say you want to get the average overall rating for each product:

• For rating 1, (9) nine people.
• For rating 2, (13) Thirteen people.
• For rating 3, (1) one people.

Using the AVERAGE function would result in an average of 7.7. Of course, this doesn’t make any sense. We should expect an average within the range of the scale (1 to 5).

In order to correctly calculate the average overall response to each question, we need to:

1. Multiply the number of individuals selecting each rating by the corresponding rating value (1 – 5)
2. Add the results of those calculations together.
3. Divide that result by the total number of responses to the question.

Example:

    SELECT
    SUM(
    case 
        WHEN FLOOR(rating) = 1 THEN rating
        WHEN FLOOR(rating) = 2 THEN rating *2
        WHEN FLOOR(rating) = 3 THEN rating *3
        WHEN FLOOR(rating) = 4 THEN rating *4
        WHEN FLOOR(rating) = 5 THEN rating *5        
    end    
    ) / SUM(rating)
    FROM tableRatings

Answer 3

Here, try this:

SAMPLE DATA

create table UserDetails(
    Id int,
    ServiceDescription varchar(20),
    Skills varchar(20)
)
create table Review(
    Id int,
    CustomerId int,
    VendorId int,
    Rating int
)

insert into UserDetails values(1, 'Plaster', 'plaster'),(2, 'construction', 'construction'),(3, 'plaster', 'plaster');
insert into Review values(1, 4, 1, 3),(2, 5, 1, 3);

SOLUTION

select
    u.Id as VendorId,
    u.ServiceDescription,
    u.Skills,
    isnull(sum(r.rating)/count(r.rating), 0) as AverageRating
from UserDetails u
left join Review r
    on r.VendorId = u.id
where
    u.ServiceDescription like '%plaster%'
    or u.Skills like '%plaster%'
group by 
    u.Id,
    u.ServiceDescription,
    u.Skills
order by AverageRating desc