Как добавить точку в колонку таблицы с Python кода?

import discord
from discord.ext import commands
import os
import asyncpg, asyncio
import psycopg2
 
PREFIX = '.'
 
database = os.environ.get('DATABASE')
user = os.environ.get('USER')
password = os.environ.get('PASSWORD')
host = os.environ.get('HOST')
port = os.environ.get('PORT')
 
conn = psycopg2.connect(
    database = f"{database}", 
    user = f"{user}", 
    password = f"{password}", 
    host = f"{host}", 
    port = "5432"
)
 
cursor = conn.cursor()
 
PREFIX=('.')
 
def is_owner_guild(ctx):
    return ctx.author.id == ctx.guild.owner.id
 
class prefix(commands.Cog):
    def __init__(self,bot):
        self.bot = bot
        
    @commands.Cog.listener()
    async def on_guild_join(self, guild):
        join_guild_id = guild.id
        cursor.execute(f'INSERT INTO public."prefixDB" (guild_id, prefix) VALUES ({join_guild_id}' + '.' + ');')
        conn.commit()
 
    @commands.Cog.listener()
    async def on_guild_remove(self,guild):
        remove_guild_id = guild.id
        cursor.execute('DELETE FROM public."prefixDB" WHERE guild_id = ' + f'{remove_guild_id}' + ';')
        conn.commit()
 
    @commands.command()
    @commands.check(is_owner_guild)
    async def prefix(self, ctx):
        cursor.execute('INSERT INTO public."prefixDB"(guild_id, prefix) VALUES (12,12);')
        conn.commit()
 
def setup(bot):
    bot.add_cog(prefix(bot))