enum conversion type has unexpected results

[jycor]

Depending on the conversion, we need to treat ENUMs as either ints or strings.

MySQL:

create table t (i int primary key, e enum('abc', 'def', 'ghi'));
insert into t values (1, 'abc'), (2, 'def'), (3, 'ghi');
select i, cast(e as char) from t;
+---+-----------------+
| i | cast(e as char) |
+---+-----------------+
| 1 | abc             |
| 2 | def             |
| 3 | ghi             |
+---+-----------------+
3 rows in set (0.0005 sec)

select i, cast(e as signed) from t;
+---+-------------------+
| i | cast(e as signed) |
+---+-------------------+
| 1 |                 1 |
| 2 |                 2 |
| 3 |                 3 |
+---+-------------------+
3 rows in set (0.0004 sec)

Dolt:

select i, cast(e as char) from t;
+---+-----------------+
| i | cast(e as char) |
+---+-----------------+
| 1 | 1               |
| 2 | 2               |
| 3 | 3               |
+---+-----------------+
3 rows in set (0.00 sec)

select i, cast(e as signed) from t;
+---+-------------------+
| i | cast(e as signed) |
+---+-------------------+
| 1 |                 1 |
| 2 |                 2 |
| 3 |                 3 |
+---+-------------------+
3 rows in set (0.0004 sec)

This also impacts CASE statements (and probably many others), as the resulting enum is converted to a string, but comes out as an int.