postgre安装和使用（R&Python)

安装postgre

http://helianthus-code.lofter.com/post/1dfe03e0_1c68233aa

这里选C更好

这里口令密码输入就是黑的

我装的时候反复报错，查了一下发现在一开始选择data为F盘时就在里面创建了一些文件，

需要回头把整个data文件夹都删掉，创建一个新的空的data文件夹，再创建一遍就成功了

换了网络后postgre启动不了

OperationalError: (psycopg2.OperationalError) could not connect to server: Connection refused (0x0000274D/10061)

Is the server running on host "127.0.0.1" and accepting

TCP/IP connections on port 5432?

办法：重启service中的 PostgreSQL

cd C:\Program Files\PostgreSQL\10\bin

pg_ctl start

start不行换pgctl_restart

添加新列

alter table schema_a.table_a add column descr varchar

如何设置自增id

看了两个小时终于解决了

先设置sequence

这个nextval设置在默认处一点用都没有，但是上面建立sequence的步骤是有用的，

之后建立以下查询并运行，是我在用英文搜索after setting sequence in postgresql the column still is null之后终于查到的，

下次遇到任何postgre问题我决定直接用英文搜stackoverflow，官方文档没解决任何问题

ALTER SEQUENCE sequence RESTART WITH 1;
UPDATE report_basic_info SET id=nextval('sequence');

两个stackoverflow链接：

https://stackoverflow.com/questions/27220139/setting-auto-increment-id-in-postgres-with-navicat

https://stackoverflow.com/questions/4678110/how-to-reset-sequence-in-postgres-and-fill-id-column-with-new-data

R&postGRE

包

library(RPostgreSQL)

然后连接数据库并规定编码

drv <- dbDriver("PostgreSQL")
con <- dbConnect(drv, host="localhost", user= "postgres", password="#", dbname="postgres")
postgresqlpqExec(con, "SET client_encoding = 'gbk'")

导入表格

com_info = dbSendQuery(con, statement = 'SELECT * FROM listed_company')
com_info <- fetch(com_info, n = -1)

往数据库存入数据

dbWriteTable(con, "MyData", MyData)

Python&postGRE

基础sqlalchemy

# 导入包
from sqlalchemy import create_engine
import pandas as pd
from string import Template
# 初始化引擎
engine = create_engine('postgresql+psycopg2://' + pg_username + ':' + pg_password + '@' + pg_host + ':' + str(
    pg_port) + '/' + pg_database)
query_sql = """
      select * from $arg1
      """
query_sql = Template(query_sql) # template方法

df = pd.read_sql_query(query_sql .substitute(arg1=tablename),engine) # 配合pandas的方法读取数据库值

# 配合pandas的to_sql方法使用十分方便（dataframe对象直接入库）
df.to_sql(table, engine, if_exists='replace', index=False) #覆盖入库
df.to_sql(table, engine, if_exists='append', index=False)  #增量入库

基础psycopg2

1.创建表

#!/usr/bin/pythonimport psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")print "Opened database successfully"

cur = conn.cursor()
cur.execute('''CREATE TABLE COMPANY
       (ID INT PRIMARY KEY     NOT NULL,
       NAME           TEXT    NOT NULL,
       AGE            INT     NOT NULL,
       ADDRESS        CHAR(50),
       SALARY         REAL);''')print "Table created successfully"

conn.commit()
conn.close()

2.插入记录

cur.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \
      VALUES (1, 'Paul', 32, 'California', 20000.00 )");

3.select

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()for row in rows:print "ID = ", row[0]print "NAME = ", row[1]print "ADDRESS = ", row[2]print "SALARY = ", row[3], "\n"print "Operation done successfully";
conn.close()

4.更新

cur.execute("UPDATE COMPANY set SALARY = 25000.00 where ID=1")
conn.commit
print "Total number of rows updated :", cur.rowcount

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()for row in rows:print "ID = ", row[0]print "NAME = ", row[1]print "ADDRESS = ", row[2]print "SALARY = ", row[3], "\n"print "Operation done successfully";
conn.close()

5.删除

cur.execute("DELETE from COMPANY where ID=2;")
conn.commit
print "Total number of rows deleted :", cur.rowcount

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()for row in rows:print "ID = ", row[0]print "NAME = ", row[1]print "ADDRESS = ", row[2]print "SALARY = ", row[3], "\n"print "Operation done successfully";
conn.close()

6.我自己的模板

# -*- coding: gbk -*-
import numpy as np
import pandas as pd
import psycopg2
from sqlalchemy import create_engine
from string import Template
import re
db_engine = create_engine('postgresql://postgres:###@127.0.0.1:5432/postgres')# 初始化引擎

x = pd.read_csv('report_basic_info.txt', delimiter="\t")
table='report_basic_info'
x.to_sql(table, db_engine, if_exists='replace', index=False)