Question

我有一个sql查询，可以从两个内连接表中进行选择。执行select语句大约需要50秒。但是，fetchall（）需要788秒，它只获取981个结果。这是查询和fetchall代码：

time0 = time.time()
self.cursor.execute("SELECT spectrum_id, feature_table_id "+
                    "FROM spectrum AS s "+
                    "INNER JOIN feature AS f "+
                    "ON f.msrun_msrun_id = s.msrun_msrun_id "+
                    "INNER JOIN (SELECT feature_feature_table_id, min(rt) AS rtMin, max(rt) AS rtMax, min(mz) AS mzMin, max(mz) as mzMax "+
                                 "FROM convexhull GROUP BY feature_feature_table_id) AS t "+
                    "ON t.feature_feature_table_id = f.feature_table_id "+
                    "WHERE s.msrun_msrun_id = ? "+
                    "AND s.scan_start_time >= t.rtMin "+
                    "AND s.scan_start_time <= t.rtMax "+
                    "AND base_peak_mz >= t.mzMin "+
                    "AND base_peak_mz <= t.mzMax", spectrumFeature_InputValues)
print 'query took:',time.time()-time0,'seconds'

time0 = time.time()
spectrumAndFeature_ids = self.cursor.fetchall()      
print time.time()-time0,'seconds since to fetchall'

为什么胎儿需要这么长时间？

更新

这样做的：

while 1:
    info = self.cursor.fetchone()
    if info:
        <do something>
    else:
        break

和

一样慢

allInfo = self.cursor.fetchall()         
for info in allInfo:
    <do something>

Answer 1

默认情况下，由于fetchall()对象的fetchone()设置为1，arraysize与Cursor的循环一样慢。

为了加快速度，你可以循环fetchmany()，但是为了看到性能提升，你需要为它提供一个大于1的大小参数，否则它将按批次{{{ 1}}，即1。

很有可能只是通过提高arraysize的值来获得性能提升，但我没有这方面的经验，所以你可能想要首先尝试这样做：

arraysize

有关上述内容的更多信息：http://docs.python.org/library/sqlite3.html#sqlite3.Cursor.fetchmany

sqlite.fetchall（）这么慢是不正常的？

更新

1 个答案: