Help With Passing Values to a Subquery

Question

Hello,
I am new to the SQL programming language. I have a fairly simple query that reads as follows:
SELECT Utility_Type,Instance_ID, WINS_Current_Amount/
(SELECT AVG
  (CASE WHEN (Corrected_Usage_Standardized IS NULL AND Extrapolated_Usage IS NOT NULL) 
THEN (WINS_Current_Amount/Extrapolated_Usage)
WHEN (Corrected_Usage_Standardized IS NOT NULL AND Extrapolated_Usage IS NULL) 
THEN (WINS_Current_Amount/Corrected_Usage_Standardized)
  END)
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
WHERE WINS_Account_Number = '021202000'
 AND (Corrected_Usage_Standardized IS NOT NULL OR Extrapolated_Usage IS NOT NULL) 
 AND (('10-01-2013' <= WINS_Invoice_Date) AND (WINS_Invoice_Date <= '09-30-2014')))
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
WHERE WINS_Account_Number = '021202000'
 AND (Corrected_Usage_Standardized IS NULL AND Extrapolated_Usage IS NULL) 
 AND (('10-01-2013' <= WINS_Invoice_Date) AND (WINS_Invoice_Date <= '09-30-2014'))
All the data I am concerned with is coming from a single table with a long-winded name (All_Utility_Data_Standardized_With_Extrapolated_Values). Essentially, the subquery takes the average of the calculated unit cost and applies that unit cost to where values
for the Current_Amount are not corrected or extrapolated. This query works great when I manually input the account number i.e. ('021202000'). But now I want to pass it 3,283 other accounts which I obtain from the following query using the same table:
SELECT DISTINCT(WINS_Account_Number)
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
WHERE Corrected_Usage_Standardized IS NULL 
    AND Extrapolated_Usage IS NULL 
    AND ((WINS_Invoice_Date > '10-01-2013') AND (WINS_Invoice_Date < '09-30-2014'))
I tried to put this query in place of '021202000' but it says that Subquery returned more than 1 value which I understand why, but I'm not sure how to fix. All I want to do is one-by-one place a new account number in the bold statement in the first query
and update a table using the calculated values. Each account may have any number of results (multiple averaged results), but I need to make sure the averaging only occurs using values specific to the account entered in bold. If that makes any sense. Anyways,
any help would be much appreciated as I am just starting to learn SQL. Thanks.
Kevin

Answer 1

Hi Kevin, 
To fix the subquery error you just need to change "=" to "IN".  
However, the query will probably run a lot faster if you use an inner join instead, like so:
SELECT Utility_Type,Instance_ID, WINS_Current_Amount/
(SELECT AVG
  (CASE WHEN (Corrected_Usage_Standardized IS NULL AND Extrapolated_Usage IS NOT NULL) 
THEN (WINS_Current_Amount/Extrapolated_Usage)
WHEN (Corrected_Usage_Standardized IS NOT NULL AND Extrapolated_Usage IS NULL) 
THEN (WINS_Current_Amount/Corrected_Usage_Standardized)
  END)
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
INNER JOIN 
SELECT DISTINCT(WINS_Account_Number)
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
WHERE Corrected_Usage_Standardized IS NULL 
AND Extrapolated_Usage IS NULL 
AND ((WINS_Invoice_Date > '10-01-2013') AND (WINS_Invoice_Date < '09-30-2014'))
) Accts ON All_Utility_Data_Standardized_With_Extrapolated_Values.WINS_Account_Number = Accts.WINS_Account_Number
 AND (Corrected_Usage_Standardized IS NOT NULL OR Extrapolated_Usage IS NOT NULL) 
 AND (('10-01-2013' <= WINS_Invoice_Date) AND (WINS_Invoice_Date <= '09-30-2014')))
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
INNER JOIN 
SELECT DISTINCT(WINS_Account_Number)
FROM All_Utility_Data_Standardized_With_Extrapolated_Values
WHERE Corrected_Usage_Standardized IS NULL 
AND Extrapolated_Usage IS NULL 
AND ((WINS_Invoice_Date > '10-01-2013') AND (WINS_Invoice_Date < '09-30-2014'))
) Accts ON All_Utility_Data_Standardized_With_Extrapolated_Values.WINS_Account_Number = Accts.WINS_Account_Number
 AND (Corrected_Usage_Standardized IS NULL AND Extrapolated_Usage IS NULL) 
 AND (('10-01-2013' <= WINS_Invoice_Date) AND (WINS_Invoice_Date <= '09-30-2014'))
Cheers
Lucas
LucasF