Python 3 无法检查数据库是否存在并创建它

问题描述

我是 Python 初学者。我想使用 Python 3 检查 sql 服务器上的 test2 数据库。如果它不存在，我将创建它。但是发现报错，不知道怎么办？

python 代码：

import pymssql 
 
 
def conn():
    ret = pymssql.connect(host='DESKTOP-4CDQomr',user = 'sa',password = '123456') 
    if ret:
        print("connect successfully!")
    else:
        print("connect Failed!")

    return ret
        

 
 
if __name__ == '__main__':
    conn = conn()  
    if conn:
        cursor = conn.cursor()
        sql = "if not exist (select * from sys.databases where name = 'test2')"
        conn.autocommit(True)
        cursor.execute(sql)
        conn.autocommit(False) 
        conn.close()

错误信息：

---------------------------------------------------------------------------
MSsqlDatabaseException                    Traceback (most recent call last)
src\pymssql.pyx in pymssql.Cursor.execute()

src\_mssql.pyx in _mssql.MSsqlConnection.execute_query()

src\_mssql.pyx in _mssql.MSsqlConnection.execute_query()

src\_mssql.pyx in _mssql.MSsqlConnection.format_and_run_query()

src\_mssql.pyx in _mssql.check_cancel_and_raise()

src\_mssql.pyx in _mssql.maybe_raise_MSsqlDatabaseException()

MSsqlDatabaseException: (156,b"Incorrect Syntax near the keyword 'select'.DB-Lib error message 20018,severity 15:\nGeneral sql Server error: Check messages from the sql Server\nDB-Lib error message 20018,severity 15:\nGeneral sql Server error: Check messages from the sql Server\n")

During handling of the above exception,another exception occurred:

OperationalError                          Traceback (most recent call last)
F:\jupyter\connect.py in <module>
     20         sql = "if not exist (select * from sys.databases where name = 'test2')"
     21         conn.autocommit(True)
---> 22         cursor.execute(sql)
     23         conn.autocommit(False)
     24         conn.close()

src\pymssql.pyx in pymssql.Cursor.execute()

OperationalError: (156,severity 15:\nGeneral sql Server error: Check messages from the sql Server\n")

解决方法

我通过修改以下代码解决了我的问题：

sql = "if not exist (select * from sys.databases where name = 'test2')"

到

sql = "if not exists (select * from sys.databases where name = 'test2') begin create database test2 end"

,

我没有安装用于测试的 MS SQL Server，但是

if not exist (select * from sys.databases where name = 'test2')

对我来说似乎不是有效的 SQL。

也许你想做这样的事情：

cur = conn.cursor()
# Check if the database already exists.
cur.execute("""SELECT COUNT(*) FROM sys.databases WHERE name = 'test2'""")
res = cur.fetchone()[0]
if res == 0:
    conn.autocommit(True)
    cur.execute("""CREATE DATABASE test2""")
    conn.autocommit(False)

另一种方法可能是尝试直接创建数据库，如果异常已经存在，则捕获异常。如果在您获取计数和发送 create 语句之间有可能由其他人创建数据库，那么这是一种更好的方法。

import sys

cur = conn.cursor()
conn.autocommit(True)
try:
    cur.execute("""CREATE DATABASE test2""")
except Exception as ex:
    # Rollback is probably unnecessary
    conn.rollback()
    print('Failed to create the database because',ex,file=sys.stderr)
finally:
    conn.autocommit(False)
    conn.close()

,

您好，希望下面的代码对您有所帮助！

import mysql.connector

DB_NAME  = "test2"

client = mysql.connector.connect(host = "127.0.0.1",user = "admin",passwd = "password")
mycursor = client.cursor()
mycursor.execute("SHOW DATABASES")

if DB_NAME in mycursor:    print("Database exists :)")
else :
    print(f"Database {DB_NAME} doesn't exist,creating now....")
    mycursor.execute("CREATE DATABASE firstdatabase")
    print(f"Database {DB_NAME} created!")