SQL query, if value is null then return 1

I have a query that is returning the exchange rate value set up in our system. Not every order will have an exchange rate (currate.currentrate) so it is returning null values.

Can I get it to return 1 instead of null?

Something like an if statement maybe:

 if isnull(currate.currentrate) then 1 else currate.currentrate 

Here is my query below. I greatly appreciate all your help!

 SELECT     orderhed.ordernum, orderhed.orderdate, currrate.currencycode,  currrate.currentrate
 FROM         orderhed LEFT OUTER JOIN
                  currrate ON orderhed.company = currrate.company AND orderhed.orderdate = currrate.effectivedate

You can use a CASE statement.

SELECT 
    CASE WHEN currate.currentrate IS NULL THEN 1 ELSE currate.currentrate END
FROM ...

You can use COALESCE:

SELECT  orderhed.ordernum, 
    orderhed.orderdate, 
    currrate.currencycode,  
    coalesce(currrate.currentrate, 1) as currentrate
FROM orderhed 
LEFT OUTER JOIN currrate 
    ON orderhed.company = currrate.company 
    AND orderhed.orderdate = currrate.effectivedate

Or even IsNull():

SELECT  orderhed.ordernum, 
    orderhed.orderdate, 
    currrate.currencycode,  
    IsNull(currrate.currentrate, 1) as currentrate
FROM orderhed 
LEFT OUTER JOIN currrate 
    ON orderhed.company = currrate.company 
    AND orderhed.orderdate = currrate.effectivedate

Here is an article to help decide between COALESCE and IsNull:

http://www.mssqltips.com/sqlservertip/2689/deciding-between-coalesce-and-isnull-in-sql-server/

SELECT 
    ISNULL(currate.currentrate, 1)  
FROM ...

is less verbose than the winning answer and does the same thing

https://msdn.microsoft.com/en-us/library/ms184325.aspx

a) If you want 0 when value is null

SELECT isnull(PartNum,0) AS PartNumber, PartID
FROM Part

b) If you want 0 when value is null and otherwise 1

SELECT 
  (CASE
    WHEN PartNum IS NULL THEN 0
    ELSE 1
  END) AS PartNumber,
  PartID
FROM Part