如何在sql命令中使用python变量

Question

So I have got the average salaries from my server, and store into a python variable and I want to know is that possible to use this variable in the later SQL common in python? and I got the avg is '51777'

connection = pymysql.connect (host = "...",
                          user = "...",
                          passwd = "...",
                          db = "...")
cursor = connection.cursor()





# select employeeID from employees table  using where, group by, and order by




cursor.execute("\
select title, avg(salaries) \
from employees group by title;")

x = cursor.fetchall()
print x


#store the value calculated from the table
cursor.execute("\
select avg(salaries) \
from employees;")

y = cursor.fetchall()
print y
z = y[0]
z = int(z[0])
print z

#using the variable into sql command
cursor.execute("select employeeID \
from employees where salaries > %s)", (z))

a = cursor.fetchall()
print a

cursor.close()
connection.close()

and the code

 #using the variable into sql command
    cursor.execute("select employeeID \
    from employees where salaries > %s)", (z))

doesn't work and I am not sure what to do next

Sorry I forgot to contain the error:

ProgrammingErrorTraceback (most recent call last)

W:\My Documents\calsses\2018 spring\MGMT 590\project\other queries.py in <module>()
     38 #using the variable into sql command
     39 cursor.execute("select employeeID \
---> 40 from employees where salaries > %s)", (z,))
     41 
     42 a = cursor.fetchall()
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\cursors.py in execute(self, query, args)
    164         query = self.mogrify(query, args)
    165 
--> 166         result = self._query(query)
    167         self._executed = query
    168         return result
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\cursors.py in _query(self, q)
    320         conn = self._get_db()
    321         self._last_executed = q
--> 322         conn.query(q)
    323         self._do_get_result()
    324         return self.rowcount
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in query(self, sql, unbuffered)
    833                 sql = sql.encode(self.encoding, 'surrogateescape')
    834         self._execute_command(COMMAND.COM_QUERY, sql)
--> 835         self._affected_rows = self._read_query_result(unbuffered=unbuffered)
    836         return self._affected_rows
    837 
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in _read_query_result(self, unbuffered)
   1017         else:
   1018             result = MySQLResult(self)
-> 1019             result.read()
   1020         self._result = result
   1021         if result.server_status is not None:
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in read(self)
   1300     def read(self):
   1301         try:
-> 1302             first_packet = self.connection._read_packet()
   1303 
   1304             if first_packet.is_ok_packet():
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in _read_packet(self, packet_type)
    979 
    980         packet = packet_type(buff, self.encoding)
--> 981         packet.check_error()
    982         return packet
    983 
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in check_error(self)
    391             errno = self.read_uint16()
    392             if DEBUG: print("errno =", errno)
--> 393             err.raise_mysql_exception(self._data)
    394 
    395     def dump(self):
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\err.py in raise_mysql_exception(data)
    105         errval = data[3:].decode('utf-8', 'replace')
    106     errorclass = error_map.get(errno, InternalError)
--> 107     raise errorclass(errno, errval)

ProgrammingError: (1064, u"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1") 

After I add triple quotes like this:

cursor.execute('''select employeeID
from employees where salaries > %s)''', (z,))

and still doesn't work Error:

ProgrammingErrorTraceback (most recent call last)
W:\My Documents\calsses\2018 spring\MGMT 590\project\other queries.py in <module>()
     38 #using the variable into sql command
     39 cursor.execute('''select employeeID
---> 40 from employees where salaries > %s)''', (z,))
     41 
     42 a = cursor.fetchall()
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\cursors.py in execute(self, query, args)
    164         query = self.mogrify(query, args)
    165 
--> 166         result = self._query(query)
    167         self._executed = query
    168         return result
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\cursors.py in _query(self, q)
    320         conn = self._get_db()
    321         self._last_executed = q
--> 322         conn.query(q)
    323         self._do_get_result()
    324         return self.rowcount
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in query(self, sql, unbuffered)
    833                 sql = sql.encode(self.encoding, 'surrogateescape')
    834         self._execute_command(COMMAND.COM_QUERY, sql)
--> 835         self._affected_rows = self._read_query_result(unbuffered=unbuffered)
    836         return self._affected_rows
    837 
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in _read_query_result(self, unbuffered)
   1017         else:
   1018             result = MySQLResult(self)
-> 1019             result.read()
   1020         self._result = result
   1021         if result.server_status is not None:
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in read(self)
   1300     def read(self):
   1301         try:
-> 1302             first_packet = self.connection._read_packet()
   1303 
   1304             if first_packet.is_ok_packet():
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in _read_packet(self, packet_type)
    979 
    980         packet = packet_type(buff, self.encoding)
--> 981         packet.check_error()
    982         return packet
    983 
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\connections.py in check_error(self)
    391             errno = self.read_uint16()
    392             if DEBUG: print("errno =", errno)
--> 393             err.raise_mysql_exception(self._data)
    394 
    395     def dump(self):
C:\Program Files\Enthought\Canopy\edm\envs\User\lib\site-packages\pymysql\err.py in raise_mysql_exception(data)
    105         errval = data[3:].decode('utf-8', 'replace')
    106     errorclass = error_map.get(errno, InternalError)
--> 107     raise errorclass(errno, errval)

ProgrammingError: (1064, u"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 2") 

Answer 1

So there are two ways I find out to solve this in python 2.7 and I think it is better to share the solution for this one. So the main reason why it fails is that I have not converted the variable into the string, in order to use the SQL command in python, we have to convert SQL command in. So there are two ways to solve this:

#1

cursor.execute('''select employeeID,FirstName, LastName
from employees where salaries > ''' + str(z) + ''';''')

#2

cursor.execute('''select employeeID,FirstName, LastName 
from employees 
where salaries > %s ;''' %(z))