How to calculate percentage with a SQL statement

1. The most efficient (using over()).

select Grade, count(*) * 100.0 / sum(count(*)) over()
from MyTable
group by Grade

2. Universal (any SQL version).

select Grade, count(*) * 100.0 / (select count(*) from MyTable)
from MyTable
group by Grade;

3. With CTE, the least efficient.

with t(Grade, GradeCount)
as
(
select Grade, count(*)
from MyTable
group by Grade
)
select Grade, GradeCount * 100.0/(select sum(GradeCount) from t)
from t;

I had a similar issue to this. you should be able to get the correct result multiplying by 1.0 instead of 100.See example Image attached

Select Grade, (Count(Grade)* 1.0 / (Select Count(*) From MyTable)) as Score From MyTable Group By Grade
![See reference image attached][1]


[1]:

This one is working well in MS SQL. It transforms varchar to the result of two-decimal-places-limited float.

Select field1, cast(Try_convert(float,(Count(field2)* 100) /
Try_convert(float, (Select Count(*) From table1))) as decimal(10,2)) as new_field_name
From table1
Group By field1, field2;

I simply use this when ever I need to work out a percentage..

ROUND(CAST((Numerator * 100.0 / Denominator) AS FLOAT), 2) AS Percentage

Note that 100.0 returns 1 decimal, whereas 100 on it's own will round up the result to the nearest whole number, even with the ROUND(...,2) function!