KSQL 5.4 Error message needs clarifying

[rmoff]

The example given in this error is not precise enough:

ksql> SELECT * FROM CUSTOMERS;
Table 'CUSTOMERS' is not materialized. KSQL currently only supports static queries on materialized aggregate tables. i.e. those created by a 'CREATE TABLE AS SELECT <fields> FROM <sources> GROUP BY <key>' style statement.

ksql> CREATE TABLE FOO AS SELECT ID, FIRST_NAME FROM CUSTOMERS_REKEYED GROUP BY ID, FIRST_NAME;
GROUP BY requires columns using aggregate functions in SELECT clause.
ksql>

We should replace the text in the message:

CREATE TABLE AS SELECT <fields> FROM <sources> GROUP BY <key>

with

CREATE TABLE AS SELECT <fields>,<aggregate_functions> FROM <sources> GROUP BY <key>