我就是看不出这个错误的原因。我在phpmyadmin中尝试过同样的sql，它运行得非常好，但在python中尝试时失败了。
带sql查询的python代码：

cursor.execute("UPDATE marketPricesAvg SET avg%sh=(SELECT AVG(price) FROM marketPrices WHERE itemName = %s AND ((NOW() - marketPrices.datetime) < %s) WHERE itemName = %s)", (time, itemName, time_sec, itemName))

错误消息：

Traceback (most recent call last):
  File "/root/marketprices/insert.py", line 42, in <module>
    calculate_avg(itemName, time)
  File "/root/marketprices/insert.py", line 29, in calculate_avg
    cursor.execute("UPDATE marketPricesAvg SET avg%sh=(SELECT AVG(price) FROM marketPrices WHERE itemName = %s AND ((NOW() - marketPrices.datetime) < %s) WHERE itemName = %s)", (time, itemName, time_sec, itemName))
  File "/usr/local/lib/python2.7/dist-packages/pymysql/cursors.py", line 170, in execute
    result = self._query(query)
  File "/usr/local/lib/python2.7/dist-packages/pymysql/cursors.py", line 328, in _query
    conn.query(q)
  File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 516, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 727, in _read_query_result
    result.read()
  File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 1066, in read
    first_packet = self.connection._read_packet()
  File "/usr/local/lib/python2.7/dist-packages/pymysql/connections.py", line 683, in _read_packet
    packet.check_error()
  File "/usr/local/lib/python2.7/dist-packages/pymysql/protocol.py", line 220, in check_error
    err.raise_mysql_exception(self._data)
  File "/usr/local/lib/python2.7/dist-packages/pymysql/err.py", line 109, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.ProgrammingError: (1064, u"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 'WHERE itemName = 'Aluminium')' at line 1")

谢谢你的建议。