SHOW WARNINGS statement can be used to retrieve the warning produced by the latest query. The error message will be returned along with the query itself:

mysql> SELECT * FROM test1 WHERE MATCH('@@title hello') \G
ERROR 1064 (42000): index test1: syntax error, unexpected TOK_FIELDLIMIT
near '@title hello'

mysql> SELECT * FROM test1 WHERE MATCH('@title -hello') \G
ERROR 1064 (42000): index test1: query is non-computable (single NOT operator)

mysql> SELECT * FROM test1 WHERE MATCH('"test doc"/3') \G
*************************** 1\. row ***************************
        id: 4
    weight: 2500
  group_id: 2
date_added: 1231721236
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS \G
*************************** 1\. row ***************************
  Level: warning
   Code: 1000
Message: quorum threshold too high (words=2, thresh=3); replacing quorum operator
         with AND operator
1 row in set (0.00 sec)

SHOW [{GLOBAL | SESSION}] VARIABLES [WHERE variable_name='xxx' | LIKE 'pattern']

It returns the current values of a few server-wide variables. Also, support for GLOBAL and SESSION clauses was added.

mysql> SHOW GLOBAL VARIABLES;
+--------------------------+-----------+
| Variable_name            | Value     |
+--------------------------+-----------+
| autocommit               | 1         |
| collation_connection     | libc_ci   |
| query_log_format         | sphinxql  |
| log_level                | info      |
| max_allowed_packet       | 134217728 |
| character_set_client     | utf8      |
| character_set_connection | utf8      |
| grouping_in_utc          | 0         |
| last_insert_id           | 123, 200  |
+--------------------------+-----------+
9 rows in set (0.00 sec)

Support for WHERE variable_name clause was added, to help certain connectors.

SHOW COLLATION

This is currently a placeholder query that does nothing and reports success. That is in order to keep compatibility with frameworks and connectors that automatically execute this statement.

mysql> SHOW COLLATION;
Query OK, 0 rows affected (0.00 sec)