将大型 Pandas 数据帧写入 SQL Server 数据库

2021-12-30 00:00:00 python pandas sqlalchemy sql-server

我有 74 个相对较大的 Pandas DataFrame(大约 34,600 行和 8 列)，我试图尽快将它们插入到 SQL Server 数据库中.在做了一些研究之后，我了解到好的 ole pandas.to_sql 函数并不适合将如此大的插入到 SQL Server 数据库中，这是我最初采用的方法(非常慢 - 将近一个小时应用程序完成，而使用 mysql 数据库时大约需要 4 分钟.)

I have 74 relatively large Pandas DataFrames (About 34,600 rows and 8 columns) that I am trying to insert into a SQL Server database as quickly as possible. After doing some research, I learned that the good ole pandas.to_sql function is not good for such large inserts into a SQL Server database, which was the initial approach that I took (very slow - almost an hour for the application to complete vs about 4 minutes when using mysql database.)

这篇文章 和许多其他 StackOverflow 帖子都帮助我指明了正确的方向，但我遇到了障碍:

This article, and many other StackOverflow posts have been helpful in pointing me in the right direction, however I've hit a roadblock:

出于上面链接中解释的原因，我正在尝试使用 SQLAlchemy 的核心而不是 ORM.所以，我将数据帧转换为字典，使用 pandas.to_dict 然后执行 execute() 和 insert():

I am trying to use SQLAlchemy's Core rather than the ORM for reasons explained in the link above. So, I am converting the dataframe to a dictionary, using pandas.to_dict and then doing an execute() and insert():

self._session_factory.engine.execute(
    TimeSeriesResultValues.__table__.insert(),
    data)
# 'data' is a list of dictionaries.

问题是插入没有得到任何值——它们显示为一堆空括号，我得到这个错误:

The problem is that insert is not getting any values -- they appear as a bunch of empty parenthesis and I get this error:

(pyodbc.IntegretyError) ('23000', "[23000] [FreeTDS][SQL Server]Cannot
insert the value NULL into the column...

我传入的字典列表中有值，所以我不知道为什么这些值没有显示出来.

There are values in the list of dictionaries that I passed in, so I can't figure out why the values aren't showing up.

这是我要离开的示例:

def test_sqlalchemy_core(n=100000):
    init_sqlalchemy()
    t0 = time.time()
    engine.execute(
        Customer.__table__.insert(),
        [{"name": 'NAME ' + str(i)} for i in range(n)]
    )
    print("SQLAlchemy Core: Total time for " + str(n) +
        " records " + str(time.time() - t0) + " secs")

推荐答案

我有一个悲伤的消息要告诉你，SQLAlchemy 实际上并没有为 SQL Server 实现批量导入，它实际上只是执行同样缓慢的单个 INSERTto_sql 正在执行的语句.我会说你最好的选择是尝试使用 bcp 命令行工具编写一些脚本.这是我过去使用过的脚本，但不能保证:

I've got some sad news for you, SQLAlchemy actually doesn't implement bulk imports for SQL Server, it's actually just going to do the same slow individual INSERT statements that to_sql is doing. I would say that your best bet is to try and script something up using the bcp command line tool. Here is a script that I've used in the past, but no guarantees: 

from subprocess import check_output, call
import pandas as pd
import numpy as np
import os

pad = 0.1
tablename = 'sandbox.max.pybcp_test'
overwrite=True
raise_exception = True
server = 'P01'
trusted_connection= True
username=None
password=None
delimiter='|'
df = pd.read_csv('D:/inputdata.csv', encoding='latin', error_bad_lines=False)



def get_column_def_sql(col):
   if col.dtype == object:
      width = col.str.len().max() * (1+pad)
      return '[{}] varchar({})'.format(col.name, int(width)) 
   elif np.issubdtype(col.dtype, float):
      return'[{}] float'.format(col.name) 
   elif np.issubdtype(col.dtype, int):
      return '[{}] int'.format(col.name) 
   else:
      if raise_exception:
         raise NotImplementedError('data type {} not implemented'.format(col.dtype))
      else:
         print('Warning: cast column {} as varchar; data type {} not implemented'.format(col, col.dtype))
         width = col.str.len().max() * (1+pad)
         return '[{}] varchar({})'.format(col.name, int(width)) 

def create_table(df, tablename, server, trusted_connection, username, password, pad):         
    if trusted_connection:
       login_string = '-E'
    else:
       login_string = '-U {} -P {}'.format(username, password)

    col_defs = []
    for col in df:
       col_defs += [get_column_def_sql(df[col])]

    query_string = 'CREATE TABLE {}
({})
GO
QUIT'.format(tablename, ',
'.join(col_defs))       
    if overwrite == True:
       query_string = "IF OBJECT_ID('{}', 'U') IS NOT NULL DROP TABLE {};".format(tablename, tablename) + query_string


    query_file = 'c:\pybcp_tempqueryfile.sql'
    with open (query_file,'w') as f:
       f.write(query_string)

    if trusted_connection:
       login_string = '-E'
    else:
       login_string = '-U {} -P {}'.format(username, password)

    o = call('sqlcmd -S {} {} -i {}'.format(server, login_string, query_file), shell=True)
    if o != 0:
       raise BaseException("Failed to create table")
   # o = call('del {}'.format(query_file), shell=True)


def call_bcp(df, tablename):   
    if trusted_connection:
       login_string = '-T'
    else:
       login_string = '-U {} -P {}'.format(username, password)
    temp_file = 'c:\pybcp_tempqueryfile.csv'

    #remove the delimiter and change the encoding of the data frame to latin so sql server can read it
    df.loc[:,df.dtypes == object] = df.loc[:,df.dtypes == object].apply(lambda col: col.str.replace(delimiter,'').str.encode('latin'))
    df.to_csv(temp_file, index = False, sep = '|', errors='ignore')
    o = call('bcp sandbox.max.pybcp_test2 in c:pybcp_tempqueryfile.csv -S "localhost" -T -t^| -r
 -c')

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