ksqlDB streams/tables are empty?

Question

I want to try using ksqlDB to count a topic's messages grouped by a column, then stream the aggregation to a new Kafka topic.

First I'd read from the topic:

CREATE STREAM "foo" (
  id BIGINT,
  col BIGINT
)
WITH (
  KAFKA_TOPIC='foo',
  FORMAT='AVRO'
);

This creates the stream successfully and I can get results using SET 'auto.offset.reset' = 'earliest'; select * from foo.

Then, I'd create the table using:

CREATE TABLE "bar"
WITH (
  KAFKA_TOPIC='bar',
  FORMAT='AVRO'
)
AS SELECT col, count(*) c
FROM foo
GROUP BY col
EMIT CHANGES

However, this table is empty.

I think for the stream, I was supposed to get the id column from the message key using id BIGINT KEY. The id is duplicated in the message key and value, but if I use id BIGINT KEY, then the stream is empty. How can I populate the table with the counts?