How can I use something stored in a DataBase? SQLite / Python - python-3.x

Question

So, I am new at DataBases and I have a question. I first made a re-search in the internet but could not find anything or actually I could not understand correctly what they were explaining. Before starting with my question I want to say that I am currently working in a Discord Bot in Python as Main Language and I am trying to create a per-server-prefix system. I have already made it once but in .JSON format. Then I heard that using .JSON to save this kind of Data is not actually good so I moved to DataBases. Now, my question is:
I have stored the guild_id and prefix in my DB, how could I use that for a per-server-prefix system? I have not tried anything yet except writing the Code to store both Texts. I would really love if anyone could explain to me not just tell me the Code! Any answer will be appreciated <3.
Main.py:
def get_prefix(client, message):
db = sqlite3.connect("main.sqlite")
cursor = db.cursor()
cursor.execute(f"SELECT prefix FROM prefixes WHERE guild_id = {message.guild.id}")
result = cursor.fetchone()
if result is None:
return "/"
else:
client = commands.Bot(command_prefix = get_prefix)
Prefixes.py (COGS):
#commands.command()
#commands.has_permissions(administrator=True)
async def prefix(self, ctx, prefix=None):
db = sqlite3.connect("main.sqlite")
cursor = db.cursor()
cursor.execute(f"SELECT prefix FROM prefixes WHERE guild_id = ?", ctx.guild.id)
result = cursor.fetchone()
if result is None:
sql = ("INSERT INTO prefixes(guild_id, prefix) VALUES(?,?)")
val = (ctx.guild.id, prefix)
await ctx.channel.send(f"{prefix}")
elif result is not None:
sql = ("UPDATE prefixes SET prefix = ? WHERE guild_id = ?")
val = (prefix, ctx.guild.id)
await ctx.channel.send(f"update `{prefix}`")
cursor.execute(sql, val)
db.commit()
cursor.close()
db.close()
That is pretty much the whole code. If you think anything should be changed or have any suggestions, answer in the comments!

Answer 1

All you need to do is, after the else, put return result. For example:
result = cursor.fetchone()
if result is None:
return "/"
else:
return result
cursor.fetchone() returns a tuple with each element requested in the row, as you only requested the prefix, it will contain just that (e.g: ("!",)) which is permitted as your command_prefix callable can return a string or tuple of strings.
Warning:
You may want to add a check to ensure that someone doesn't specify an empty string (A zero length string with nothing in it) as their prefix, otherwise your bot will attempt to run every message it sees as a command
References: discord.ext.commands.Bot.command_prefix