如何从psycopg2游标获取列名称列表？

Question

我想要一个通用的方法来直接从选定的列名称生成列标签，并回想一下，看到python的psycopg2模块支持此功能。

Answer 1

从“编程的Python”由马克·鲁茨：

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

Answer 2

要获得一个单独的查询的列名，您可以查询INFORMATION_SCHEMA.COLUMNS表。在同一个查询的数据行

#!/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)) 

要获得列名，你可以使用光标的描述字段：

#!/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

我注意到，你必须在查询后使用cursor.fetchone()获得cursor.description列的列表（即[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

我人所以曾经面临类似的问题。我用一个简单的技巧来解决这个问题。 假设你像

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

然后列表有列名，你可以做以下

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

Answer 6

执行SQL查询写下面写在2.7

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

Answer 7

如果你想python脚本后从db查询命名为obj obj，可以使用以下代码片段：

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)) 

这allowes你，好像他们是类属性，即

record.id，record.other_table_column_name等

，甚至更短的以评估记录值

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

Answer 8

你可以做的另一件事是创建一个游标，你将能够通过他们的名字来引用你的列（这是一个需求，导致我到这个页面第一个地方）：

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