flink ought to implicitly cast result of avg() (et al) to float or similar

[nparrish42]

I don't think it's unreasonable to expect some sort of intelligent autocasting...

Flink SQL> select avg(c) from tiny;
+----+-------------+
| op |      EXPR$0 |
+----+-------------+
| +I |          49 |
+----+-------------+
Received a total of 1 row

Flink SQL> select avg(cast(c as float)) from tiny;
+----+--------------------------------+
| op |                         EXPR$0 |
+----+--------------------------------+
| +I |                           49.5 |
+----+--------------------------------+
Received a total of 1 row

Flink SQL> select stddev(c) from tiny;
+----+-------------+
| op |      EXPR$0 |
+----+-------------+
| +I |          23 |
+----+-------------+

Flink SQL> select stddev(cast(c as float)) from tiny;
+----+--------------------------------+
| op |                         EXPR$0 |
+----+--------------------------------+
| +I |                      23.334524 |
+----+--------------------------------+
Received a total of 1 row