How to save results of postgresql to csv/excel file using psycopg2?

Question

I use driving_distance in postgresql to find distances between all nodes, and here's my python script in pyscripter,

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,

[(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,

• 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？

I am working with postgresql 8.4, python 2.7.6 under Windows 8.1 x64.

---

Update#1: I tried the following code provided by Talvalin(thanks!),

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,

>>> 

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.

Answer 1

Based on Psycopg2's cursor.copy_expert() and Postgres COPY documentation 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.

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()