Rounding of the numeric values - sql

Question

I want to round of the values of two columns:
select a.region as "Regions",
a.suminsured,2 as "SumInsured" ,
a.suminsured/b.sum*100 as pct
from (
SELECT region, sum(suminsured) as suminsured
FROM "Exposure_commune" group by region
) a,
(select sum(suminsured) FROM "Exposure_commune") b
I want the suminsured and pct columns to come with 2 decimal places. Can someone tell me what I should do?

Answer 1

You can use directly numeric with two parameters. Second parameter for round decimal.
select sum(column_name::numeric(10,2)) from tablename

Answer 2

Use round() with two parameters, which only works for the data type numeric.
While being at it, your query can be simpler and faster:
SELECT region
, round(sum(suminsured), 2) AS suminsured
, round((sum(suminsured) * 100) / sum(sum(suminsured)) OVER (), 2) AS pct
FROM "Exposure_commune"
GROUP BY 1;
You can use sum() as window function to get the total without additional subquery, which is cheaper. Related:
Postgres window function and group by exception
Multiplying first is typically cheaper and more exact (although that barely matters with numeric).
Data type is not numeric
For data types double precision of real
You can ...
just cast to numeric to use the same function.
multiply by 100, cast to integer and divide by 100.0.
multiply by 100 and use the simple round() and devide by 100.
The simple round() with just one parameter works for floating point types as well.
Demonstrating all three variants:
SELECT region
, round(sum(suminsured), 2) AS suminsured
, (sum(suminsured) * 100)::int / 100.0 AS suminsured2
, round(sum(suminsured) * 100) / 100 AS suminsured3
, round((sum(suminsured) * 100) / sum(sum(suminsured)) OVER (), 2) AS pct
, ((sum(suminsured) * 10000) / sum(sum(suminsured)) OVER ())::int / 100.0 AS pct2
, round((sum(suminsured) * 10000) / sum(sum(suminsured)) OVER ()) / 100 AS pct3
FROM "Exposure_commune"
GROUP BY 1;
SQL Fiddle.