Except command doesn't work in SQL I am trying to make an except in SQL but it doesnt exclude the data even though they are identical.

SELECT A.payment_id,
                            SUM(A.importe_trx) monto_total
FROM  [dbo].[ABONOS] A
WHERE payment_id = '980190391415704'
GROUP BY A.payment_id

SELECT B.payment_id payment_id,
                            SUM(B.precio_venta) monto_total
FROM [dbo].[SALES_VISANET_USD] B
WHERE payment_id = '980190391415704'
GROUP BY B.payment_id


I used that query to get the data and it's the same, but it doesn't exclude it with the EXCEPT command in the middle

SELECT A.payment_id,
                            SUM(A.importe_trx) monto_total
FROM  [dbo].[ABONOS] A
WHERE payment_id = '980190391415704'
GROUP BY A.payment_id

EXCEPT

SELECT B.payment_id payment_id,
                            SUM(B.precio_venta) monto_total
FROM [dbo].[SALES_VISANET_USD] B
WHERE payment_id = '980190391415704'
GROUP BY B.payment_id


I use "sum" because in one of the tables it has different amounts with the same payment_id, but when adding and grouping them they give the same amount and the same data as the other table.
From you comment:  


  "importe_trx" and "precio_venta" stores the same data (float) that are the prices


That means you are using float data type to store these numerical values.
Problem with the float data type is that it always store rounded values, it can not precisely represent decimal values. Each values is saved as (0 or 1)*1/2+(0 or 1)*1/4+(0 or 1)*1/8+..., so 18.42 + 24.56 can be 42.98000000001 in float terms. SSMS will round these numbers, so you will not see the difference.

To fix this problem you should use decimal data type. Never use floats in any accounting data.