如何使用 psycopg2 将 postgresql 的结果保存到 csv/excel 文件？
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How to save results of postgresql to csv/excel file using psycopg2?
提问by Heinz
I use driving_distancein postgresql to find distances between all nodes, and here's my python script in pyscripter,
我在 postgresql 中使用drive_distance来查找所有节点之间的距离，这是我在 pyscripter 中的 python 脚本，
import sys
#set up psycopg2 environment
import psycopg2
#driving_distance module
query = """
select *
from driving_distance ($$
select
gid as id,
start_id::int4 as source,
end_id::int4 as target,
shape_leng::double precision as cost
from network
$$, %s, %s, %s, %s
)
;"""
#make connection between python and postgresql
conn = psycopg2.connect("dbname = 'routing_template' user = 'postgres' host = 'localhost' password = '****'")
cur = conn.cursor()
#count rows in the table
cur.execute("select count(*) from network")
result = cur.fetchone()
k = result[0] + 1
#run loops
rs = []
i = 1
while i <= k:
cur.execute(query, (i, 1000000, False, False))
rs.append(cur.fetchall())
i = i + 1
#print result
for record in rs:
print record
conn.close()
The result is fine, and part of the it in python interpreter looks like this,
结果很好，python解释器中的一部分看起来像这样，
[(1, 2, 35789.4069722436), (2, 2, 31060.0761437413), (3, 19, 30915.1312550546), (4, 3, 33438.0715007666), (5, 4, 29149.0894812718), (6, 7, 25504.020006665), (7, 7, 29594.741802956), (8, 5, 20736.2427352646), (9, 10, 19545.809601197), (10, 8, 22609.5146670393), (11, 9, 14134.5400189648), (12, 11, 12266.7845493204), (13, 18, 17426.7449057031), (14, 21, 11754.7277029158), (15, 18, 13128.3548040769), (16, 20, 21924.2253916803), (17, 11, 15209.9969992088), (18, 20, 26316.7797545076), (19, 13, 604.414419026164), (20, 16, 740.652673783403), (21, 15, 0.0), (22, 15, 2378.768084459)]
[(1, 2, 38168.1750567026), (2, 2, 33438.8442282003), (3, 19, 33293.8993395136), (4, 3, 35816.8395852256), (5, 4, 31527.8575657308), (6, 7, 27882.788091124), (7, 7, 31973.509887415), (8, 5, 23115.0108197236), (9, 10, 21924.577685656), (10, 8, 24988.2827514983), (11, 9, 16513.3081034238), (12, 11, 14645.5526337793), (13, 18, 19805.5129901621), (14, 21, 14133.4957873748), (15, 18, 15507.1228885359), (16, 20, 24302.9934761393), (17, 11, 17588.7650836678), (18, 20, 28695.5478389666), (19, 13, 2983.18250348516), (20, 16, 3119.4207582424), (21, 15, 2378.768084459), (22, 15, 0.0)]
I want to export these results to a new csv or excel files, and I have looked these related post and website,
我想将这些结果导出到一个新的 csv 或 excel 文件中，我查看了这些相关的帖子和网站，
- PostgreSQL: export resulting data from SQL query to Excel/CSV
- save (postgres) sql output to csv file
- Psycopg 2.5.3.dev0 documentation
But still can't export these working under pyscripter, how can I do？
但是在pyscripter下还是不能导出这些，怎么办？
I am working with postgresql 8.4, python 2.7.6 under Windows 8.1 x64.
我正在 Windows 8.1 x64 下使用 postgresql 8.4、python 2.7.6。
Update#1:I tried the following code provided by Talvalin(thanks!),
更新#1：我尝试了 Talvalin 提供的以下代码（谢谢！），
import sys
#set up psycopg2 environment
import psycopg2
#driving_distance module
query = """
select *
from driving_distance ($$
select
gid as id,
start_id::int4 as source,
end_id::int4 as target,
shape_leng::double precision as cost
from network
$$, %s, %s, %s, %s
)
"""
#make connection between python and postgresql
conn = psycopg2.connect("dbname = 'TC_routing' user = 'postgres' host = 'localhost' password = '****'")
cur = conn.cursor()
outputquery = 'copy ({0}) to stdout with csv header'.format(query)
with open('resultsfile', 'w') as f:
cur.copy_expert(outputquery, f)
conn.close()
But got error below,
但在下面出现错误，
>>>
Traceback (most recent call last):
File "C:/Users/Heinz/Desktop/python_test/driving_distance_loop_test.py", line 27, in <module>
cur.copy_expert(outputquery, f)
ProgrammingError: 錯誤: 在"語法錯誤"附近發生 %
LINE 10: $$, %s, %s, %s, %s
^
Maybe I need to add something more in the code above.
也许我需要在上面的代码中添加更多内容。
回答by Talvalin
Based on Psycopg2's cursor.copy_expert()and Postgres COPYdocumentation and your original code sample, please try this out. I tested a similar query export on my laptop, so I'm reasonably confident this should work, but let me know if there are any issues.
根据Psycopg2 的 cursor.copy_expert()和Postgres COPY文档以及您的原始代码示例，请尝试一下。我在我的笔记本电脑上测试了一个类似的查询导出，所以我有理由相信这应该可以工作，但如果有任何问题，请告诉我。
import sys
#set up psycopg2 environment
import psycopg2
#driving_distance module
#note the lack of trailing semi-colon in the query string, as per the Postgres documentation
query = """
select *
from driving_distance ($$
select
gid as id,
start_id::int4 as source,
end_id::int4 as target,
shape_leng::double precision as cost
from network
$$, %s, %s, %s, %s
)
"""
#make connection between python and postgresql
conn = psycopg2.connect("dbname = 'routing_template' user = 'postgres' host = 'localhost' password = 'xxxx'")
cur = conn.cursor()
outputquery = "COPY ({0}) TO STDOUT WITH CSV HEADER".format(query)
with open('resultsfile', 'w') as f:
cur.copy_expert(outputquery, f)
conn.close()
