Google BigQuery CASE function

I'm trying to run a query like what's answered here, SQL Selecting multiple sums?

SELECT  SUM(CASE WHEN order_date >= '01/01/09' THEN quantity ELSE 0 END) AS items_sold_since_date,
    SUM(quantity) AS items_sold_total,
    product_ID
FROM    Sales
GROUP BY product_ID

But if I try that, I get the error message

"message": "Unrecognized function CASE".

If I try a much more simple (from an sql tutorial),

SELECT CASE 1 WHEN 1 THEN 'one' WHEN 2 THEN 'two' ELSE 'more' END;

I then get

"message": "searched case expression not supported at: 1.8 - 1.65".

I'm going to take a wild stab in the dark and assume that the SQL CASE function is overall just not supported on BigQuery, but really hope that I'm wrong because it makes a huge bit of difference based on the report queries I want to run.