I just stumbled over this:
mysql> select "abc" = 0;
+-----------+
| "abc" = 0 |
+-----------+
| 1 |
+-----------+
1 row in set, 1 warning (0.06 sec)
mysql> show warnings;
+---------+------+-----------------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'abc' |
+---------+------+-----------------------------------------+
1 row in set (0.06 sec)
What's happening here? Where are the implicit type casts documented?