如何在pd.read_sql_query中一次执行多个SQL命令？

Question

让我创建一个用例来讨论。

CREATE  DATABASE sample;
USE sample;
CREATE TABLE quote (
  `id` int(2) unsigned NOT NULL AUTO_INCREMENT,
  `code` text ,
  `date` date DEFAULT NULL,
  `close` double DEFAULT NULL,
  PRIMARY KEY (`id`)
) ;

INSERT INTO quote (`code`, `date`, `close`)
VALUES ('epm', '20200824', 2.64); 
INSERT INTO quote (`code`, `date`, `close`)
VALUES ('dss', '20200824', 6.4); 

使用 sqlalchemy 只执行一个 sql 命令很简单。

import pandas as pd 
from sqlalchemy import create_engine
user = 'root'
mysql_pass = 'your mysql passwd'
mysql_ip = '127.0.0.1'
engine = create_engine("mysql+pymysql://{}:{}@{}:3306".format(user,mysql_pass,mysql_ip))
cmd_one_line_sql = 'select * from sample.quote;'
df = pd.read_sql_query(cmd_one_line_sql,con = engine)
df 
   id code        date  close
0   1  epm  2020-08-24   2.64
1   2  dss  2020-08-24   6.40

我得到了想要的结果，现在cmd包含多个sql命令，为了简单起见，它只包含两行

cmd_multi_lines_sql = 'use sample;select * from quote;'

刚刚cmd_multi_lines_sql分裂cmd_one_line_sql成两半。
我根据手册重写了代码片段：
用sqlalchemy执行许多sql命令

import pandas as pd
from sqlalchemy import create_engine
user = 'root'
mysql_pass = 'your mysql passwd'
mysql_ip = '127.0.0.1'
engine = create_engine("mysql+pymysql://{}:{}@{}:3306".format(user,mysql_pass,mysql_ip))
connection = engine.raw_connection()
cmd_multi_lines_sql = 'use sample;select * from quote;'
try:
    cursor = connection.cursor()
    cursor.execute(cmd_multi_lines_sql)
    results_one = cursor.fetchall()
finally:
    connection.close()

获取以下错误信息：

Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "/usr/local/lib/python3.5/dist-packages/pymysql/cursors.py", line 170, in execute
    result = self._query(query)
  File "/usr/local/lib/python3.5/dist-packages/pymysql/cursors.py", line 328, in _query
    conn.query(q)
  File "/usr/local/lib/python3.5/dist-packages/pymysql/connections.py", line 517, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/usr/local/lib/python3.5/dist-packages/pymysql/connections.py", line 732, in _read_query_result
    result.read()
  File "/usr/local/lib/python3.5/dist-packages/pymysql/connections.py", line 1075, in read
    first_packet = self.connection._read_packet()
  File "/usr/local/lib/python3.5/dist-packages/pymysql/connections.py", line 684, in _read_packet
    packet.check_error()
  File "/usr/local/lib/python3.5/dist-packages/pymysql/protocol.py", line 220, in check_error
    err.raise_mysql_exception(self._data)
  File "/usr/local/lib/python3.5/dist-packages/pymysql/err.py", line 109, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'select * from quote' at line 1")

另一种尝试：

vim  /tmp/test.sql
use sample;
select * from quote;

#write the commands in `/tmp/test.sql`
f = open('/tmp/test.sql','r')
cmd = f.read() 
df = pd.read_sql_query(cmd, con = engine)

它输出相同的错误信息。如何修复它？

Answer 1

经过一番研究并在 github 上询问后，答案是显而易见的

你需要传递所需的参数

connect_args=

以及 sqlalchemy 以来的参数

是

{"client_flag": MULTI_STATEMENTS}

所以你的Python代码和他的一样锁

from sqlalchemy import create_engine
import pymysql
from pymysql.constants.CLIENT import MULTI_STATEMENTS
user = 'root'
mysql_pass = 'testpassword'
mysql_ip = 'localhost'
cmd = 'SELECT * FROM table1;SELECT * FROM test'

engine = create_engine("mysql+pymysql://{}:{}@{}:3306/testdb1?charset=utf8".format(user,mysql_pass,mysql_ip),connect_args={"client_flag": MULTI_STATEMENTS})
connection = engine.raw_connection()

try:
    cursor = connection.cursor()
    cursor.execute(cmd)
    results_one = cursor.fetchall()
    cursor.nextset()
    results_two = cursor.fetchall()
    cursor.close()
finally:
    connection.close()

但使用此解决方案时，您需要事先知道要运行哪些查询。

如果想更灵活，用动态sql语句

from sqlalchemy import create_engine
user = 'root'
mysql_pass = 'testpassword'
mysql_ip = 'localhost'
cmd = 'SELECT * FROM table1;SELECT * FROM test'
engine = create_engine("mysql+pymysql://{}:{}@{}:3306/testdb1?charset=utf8".format(user,mysql_pass,mysql_ip))
connection = engine.raw_connection()
splitstring = cmd.split(";")
ges_resultset = []
try:
    cursor = connection.cursor()
    for cmdoneonly in splitstring:
        cursor.execute(cmdoneonly)
        results = cursor.fetchall()
        ges_resultset.append(results) 
    cursor.close()
finally:
    connection.close()

您可以在其中检查每个命令并了解 python 如何对其做出反应

• SELECT 需要获取结果集
• INSERT DELETE CREATE 你不会（还有更多，但你明白要点了）