Working with dates in Oracle SQL

Question

I am very new when it comes to using SQL and what I am attempting to do is select the waterUsage and electrcityUsage using only the month and year and select the waterUsage and

Answer 1

Assuming that billingdate is a DATE column.

You can't compare a DATE with a string value. If you only want to compare "parts" of a date you need to convert the date to a string:

select electrcityUsage, waterUsage 
from monthlyBill
where accountNumber ='211' 
  and to_char(billingDate,'MM-YY') = '12-12'

But I would strongly recommend to always use four digit years:

select electrcityUsage, waterUsage 
from monthlyBill
where accountNumber ='211' 
  and to_char(billingDate,'MM-YYYY') = '12-2012'

or use the extract function:

select electrcityUsage, waterUsage 
from monthlyBill
where accountNumber ='211' 
  and extract(month from billingDate) = 12 
  and extract(year from billingdate) = 2012;

To get the previous year, subtract a year, but you need to take into account that in Oracle a DATE always contains a time as well (despite the name of the data type). To set the time to 00:00:00 use trunc()

select electrcityUsage, waterUsage 
from monthlyBill
where accountNumber ='211' 
  and trunc(billingdate) = trunc(sysdate - interval '1' year);