How to evaluate an expression repeatedly for benchmark testing using the BENCHMARK() function?

BENCHMARK(count, exp) is a MySQL built-in function that evaluates an expression repeatedly for benchmark testing and returns 0. For example:

SELECT BENCHMARK(1000000, AES_ENCRYPT('hello','goodbye'));
  -- +----------------------------------------------------+
  -- | BENCHMARK(1000000, AES_ENCRYPT('hello','goodbye')) |
  -- +----------------------------------------------------+
  -- |                                                  0 |
  -- +----------------------------------------------------+
  -- 1 row in set (0.39 sec)

SELECT BENCHMARK(1000000, AES_ENCRYPT('hello','goodbye'));
  -- +----------------------------------------------------+
  -- | BENCHMARK(1000000, AES_ENCRYPT('hello','goodbye')) |
  -- +----------------------------------------------------+
  -- |                                                  0 |
  -- +----------------------------------------------------+
  -- 1 row in set (0.41 sec)

Note that the input expression can be a SELECT statement as long as it returns one row with one column. For example,

SELECT BENCHMARK(1000000, (SELECT name FROM mysql.help_topic LIMIT 1));
  -- +-----------------------------------------------------------------+
  -- | BENCHMARK(1000000, (SELECT name FROM mysql.help_topic LIMIT 1)) |
  -- +-----------------------------------------------------------------+
  -- |                                                               0 |
  -- +-----------------------------------------------------------------+
1 row in set (0.03 sec)

SELECT BENCHMARK(1000000, (SELECT * FROM mysql.help_topic LIMIT 1));
ERROR 1241 (21000): Operand should contain 1 column(s)

SELECT BENCHMARK(1000000, (SELECT name FROM mysql.help_topic));
ERROR 1242 (21000): Subquery returns more than 1 row

CREATE TABLE MyTable (id INTEGER, count INTEGER);

SELECT BENCHMARK(100, (INSERT INTO MyTable VALUES(1,1)));
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual 
that corresponds to your MySQL server version for the right syntax 
to use near 'INTO MyTable VALUES(1,1)))' at line 1

Reference information of the BENCHMARK() function:

BENCHMARK(count, exp): int
  Evaluates an expression repeatedly for benchmark testing.

Arguments, return value and availability:
  count: Required. The number of time to evaluate the expression.
  exp: Required. The expression to be executed.
  int: Return value. 0 if evaluations are performed successfully.
  Available since MySQL 4.0.

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