运行的时候总是出现:
/home/server/y/envs/kuanke/lib/python2.7/site-packages/sqlalchemy/sql/default_comparator.py:153: SAWarning: The IN-predicate on "STK_DIVIDEND.SYMBOL" was invoked with an empty sequence. This results in a contradiction, which nonetheless can be expensive to evaluate. Consider alternative strategies for improved performance.
'strategies for improved performance.' % expr)
什么原因呢?性能太慢?会影响结果吗?