PostgreSQL Percentage

First, you need a query that returns the sum of all values in the valor_convenio column. The query would then be simple:

select
    sum (valor_convenio) as total
from paraiba.vigente
WHERE
    convenente LIKE '%(MUNICIPAL)%'

In addition, you already have the query that adds the valor_convenio grouped by municipality (I did some alias modifications because the query did not execute the way you wrote it):

SELECT
    nome_municipio,
    SUM(valor_convenio) as total
FROM paraiba.vigente
WHERE
    convenente LIKE '%(MUNICIPAL)%'
GROUP BY nome_municipio
ORDER BY total DESC;

What is needed now is to simply merge the queries so that you get the percentage value. For this, a join can be used. It basically serves to merge complex query results. So adding the junction would look something like:

SELECT
    nome_municipio,
    SUM(valor_convenio),
    SUM(valor_convenio) / total.total AS total
FROM paraiba.vigente, (
    select sum (valor_convenio) as total 
    from paraiba.vigente 
    WHERE convenente LIKE '%(MUNICIPAL)%'
) total 
WHERE convenente LIKE '%(MUNICIPAL)%' 
GROUP BY nome_municipio 
ORDER BY total DESC;

If you run the above query, you will encounter the following error:

  

ERROR: column "total.total" must appear in the GROUP BY clause or be used in an aggregate function   LINE 1: ... nicipio, SUM (value_convenio), SUM (value_convenio) / total.tota ...

The problem is that there is a SUM grouping function with 2 different query results, and this needs to be added in a group by clause so that the information can be aggregated by the function. Since the value of the total sum of the valor_convenio column is unique for all counties, you can add it to the group by class with no impact on the final result. So you would have something like:

SELECT 
    nome_municipio, 
    SUM(valor_convenio),
    SUM(valor_convenio) / total.total AS total 
FROM paraiba.vigente, (
    select sum (valor_convenio) as total 
    from paraiba.vigente
    WHERE convenente LIKE '%(MUNICIPAL)%'
) total 
WHERE convenente LIKE '%(MUNICIPAL)%'
GROUP BY nome_municipio, total.total 
ORDER BY total DESC;

To adjust the query by adding a percentage format, you can do something like the example below, using the round rounding function and the string concatenation operator || :

SELECT 
    nome_municipio,
    SUM(valor_convenio),
    round((SUM(valor_convenio)/total.total)*100, 2) || '%' AS total
FROM paraiba.vigente, (
    select sum (valor_convenio) as total  
    from paraiba.vigente 
    WHERE convenente LIKE '%(MUNICIPAL)%'
) total
WHERE convenente LIKE '%(MUNICIPAL)%'
GROUP BY nome_municipio, total.total
ORDER BY total DESC;

Tip: Whenever you have complex queries to build, construct each piece separately and then think about the logic of joining them together. This makes it much easier to solve such problems.