Wie bekomme ich eine Liste von Spaltennamen von einem psycopg2 Cursor?

Question

Ich möchte eine allgemeine Möglichkeit, Spaltenbeschriftungen direkt aus den ausgewählten Spaltennamen zu generieren, und erinnern Sie sich daran, dass Python psycopg2 Modul diese Funktion unterstützt.

Answer 1

Von "Programming Python" von Mark Lutz:

curs.execute("Select * FROM people") 
colnames = [desc[0] for desc in curs.description] 

Answer 2

Um erhalten die Spaltennamen in einer separaten Abfrage, können Sie die information_schema.columns Tabelle abfragen.

#!/usr/bin/env python3 

import psycopg2 

if __name__ == '__main__': 
    DSN = 'host=YOUR_DATABASE_HOST port=YOUR_DATABASE_PORT dbname=YOUR_DATABASE_NAME user=YOUR_DATABASE_USER' 

    column_names = [] 

    with psycopg2.connect(DSN) as connection: 
     with connection.cursor() as cursor: 
      cursor.execute("select column_name from information_schema.columns where table_schema = 'YOUR_SCHEMA_NAME' and table_name='YOUR_TABLE_NAME'") 
      column_names = [row[0] for row in cursor] 

    print("Column names: {}\n".format(column_names)) 

Um get Spaltennamen in der gleichen Abfrage als Datenzeilen, können Sie das Beschreibungsfeld des Cursors verwenden:

#!/usr/bin/env python3 

import psycopg2 

if __name__ == '__main__': 
    DSN = 'host=YOUR_DATABASE_HOST port=YOUR_DATABASE_PORT dbname=YOUR_DATABASE_NAME user=YOUR_DATABASE_USER' 

    column_names = [] 
    data_rows = [] 

    with psycopg2.connect(DSN) as connection: 
    with connection.cursor() as cursor: 
     cursor.execute("select field1, field2, fieldn from table1") 
     column_names = [desc[0] for desc in cursor.description] 
     for row in cursor: 
     data_rows.append(row) 

    print("Column names: {}\n".format(column_names)) 

Answer 3

Ich habe bemerkt, dass Sie cursor.fetchone() nach der Abfrage verwenden müssen holen Sie sich die Liste der Spalten in cursor.description (dh in [desc[0] for desc in curs.description])

Answer 4

#!/usr/bin/python 
import psycopg2 
#note that we have to import the Psycopg2 extras library! 
import psycopg2.extras 
import sys 

def main(): 
    conn_string = "host='localhost' dbname='my_database' user='postgres' password='secret'" 
    # print the connection string we will use to connect 
    print "Connecting to database\n ->%s" % (conn_string) 

    # get a connection, if a connect cannot be made an exception will be raised here 
    conn = psycopg2.connect(conn_string) 

    # conn.cursor will return a cursor object, you can use this query to perform queries 
    # note that in this example we pass a cursor_factory argument that will 
    # dictionary cursor so COLUMNS will be returned as a dictionary so we 
    # can access columns by their name instead of index. 
    cursor = conn.cursor(cursor_factory=psycopg2.extras.DictCursor) 

    # tell postgres to use more work memory 
    work_mem = 2048 

    # by passing a tuple as the 2nd argument to the execution function our 
    # %s string variable will get replaced with the order of variables in 
    # the list. In this case there is only 1 variable. 
    # Note that in python you specify a tuple with one item in it by placing 
    # a comma after the first variable and surrounding it in parentheses. 
    cursor.execute('SET work_mem TO %s', (work_mem,)) 

    # Then we get the work memory we just set -> we know we only want the 
    # first ROW so we call fetchone. 
    # then we use bracket access to get the FIRST value. 
    # Note that even though we've returned the columns by name we can still 
    # access columns by numeric index as well - which is really nice. 
    cursor.execute('SHOW work_mem') 

    # Call fetchone - which will fetch the first row returned from the 
    # database. 
    memory = cursor.fetchone() 

    # access the column by numeric index: 
    # even though we enabled columns by name I'm showing you this to 
    # show that you can still access columns by index and iterate over them. 
    print "Value: ", memory[0] 

    # print the entire row 
    print "Row: ", memory 

if __name__ == "__main__": 
    main() 

Answer 5

I al so gewohnt, ähnliches Problem zu begegnen. Ich benutze einen einfachen Trick, um das zu lösen. Angenommen, Sie wie

in einer Liste Spaltennamen haben

col_name = ['a', 'b', 'c'] 

Dann können Sie in 2,7

total_fields = len(cursor.description)  
fields_names = [i[0] for i in cursor.description 
    Print fields_names 

Answer 6

Nach der Ausführung Wenn Sie möchten, Um namedtuple obj von db query zu haben, können Sie das folgende Snippet verwenden:

from collections import namedtuple 

def create_record(obj, fields): 
    ''' given obj from db returns namedtuple with fields mapped to values ''' 
    Record = namedtuple("Record", fields) 
    mappings = dict(zip(fields, obj)) 
    return Record(**mappings) 

cur.execute("Select * FROM people") 
colnames = [desc[0] for desc in cur.description] 
rows = cur.fetchall() 
cur.close() 
result = [] 
for row in rows: 
    result.append(create_record(row, colnames)) 

Diese allowes Sie Bestwerte zu bewerten, als ob sie Klasse Eigenschaften, dh

record.id, record.other_table_column_name usw.

oder noch kürzer

from psycopg2.extras import NamedTupleCursor 
with cursor(cursor_factory=NamedTupleCursor) as cur: 
    cur.execute("Select * ...") 
    return cur.fetchall() 

Answer 7

geschrieben SQL-Abfrage schreiben folgende Python-Skript, gehen Sie wie folgt

for row in cursor.fetchone(): 
    print zip(col_name, row) 

Answer 8

Eine andere Sache, die Sie tun können, ist, einen Cursor zu erstellen, mit dem Sie Ihre Spalten nach ihren Namen referenzieren können (das ist ein Bedürfnis, das mich zu dieser Seite geführt hat) der erste Platz):

import psycopg2 
from psycopg2.extras import RealDictCursor 

ps_conn = psycopg2.connect(...) 
ps_cursor = psql_conn.cursor(cursor_factory=RealDictCursor) 

ps_cursor.execute('select 1 as col_a, 2 as col_b') 
my_record = ps_cursor.fetchone() 
print (my_record['col_a'],my_record['col_b']) 

>> 1, 2