new String[128];//Declaring the string.

public OnPlayerConnect(playerid)
{
    GetPlayerName(playerid,namevar,24);//Make sure you already defined the variable that stores the player's name.
    if(strfind(namevar,"The clan tag will go here: example '[mG]' ",true) != -1)//Change to the your clan tag.
    {
        format(String,76,"SELECT Name FROM clanmembers WHERE Name='%s' LIMIT 1",escapename);//Selecting the Name field from the "clanmembers" table.
        mysql_query(String);
        mysql_store_result();//Storing the result.
        if(mysql_num_rows() != 0)//If the name was found in the table, then we can give the player a warm welcome.
        {
            mysql_free_result();//Remember to free the result, or you'll get lag issues.
            SendClientMessage(playerid,-1,"Nice, you're in the clan.");//Warm welcome :)
        }
        if(mysql_num_rows() == 0)//Now, if the player's name was not found in the clan table, then take the following actions:
        {
            mysql_free_result();//Free the result.
            format(String,sizeof(String),"%s has been kicked from the server. Reason: Not in clan.",GetName(playerid));
            SendClientMessageToAll(-1,String);
            Kick(playerid);//Kicking the player.
            return 1;
        }
    }
    return 1;
}

COMMAND:setclanmember(playerid, params[])
{
    if(!IsPlayerAdmin(playerid))return 0;//Checking if the player is a RCON admin.
    new id;
    if(sscanf(params,"u",id))return SendClientMessage(playerid,-1,"Usage: /setclanmember [id]");//Using sscanf to check if the params where filled.
    GetPlayerName(id,namevar,24);//Again, getting the player's name, and storing it into the name variable.
    format(String,sizeof(String),"SELECT Name FROM clanmembers WHERE Name='%s' LIMIT 1",namevar);//Selecting the name from the table.
    mysql_query(String);
    mysql_store_result();//Storing the result.
    if(mysql_num_rows() != 0)return (mysql_free_result() && SendClientMessage(playerid,-1,"That player is already in the clan."));//Freeing the result, and making sure you don't add that name again.
    mysql_free_result();//Freeing the result.
    format(String,sizeof(String),"INSERT INTO clanmembers (Name) VALUES ('%s')",namevar);//If the name was not found, then insert it into the table.
    mysql_query(String);
    format(String,sizeof(String),"You've accepted %s into the clan.",namevar);//
    SendClientMessage(playerid,-1,String);
    GetPlayerName(playerid,namevar,24);//Getting your name (user of the command)
    format(String,sizeof(String),"You've been accepted into the clan by admin %s.",namevar);
    SendClientMessage(id,-1,String);
    return 1;
}

COMMAND:removeclanmember(playerid, params[])
{
    if(!IsPlayerAdmin(playerid))return 0;//Checking if the player is a RCON admin.
    if(sscanf(params,"s",params))return SendClientMessage(playerid,-1,"Usage: /removeclanmember [name]");
    format(String,76,"SELECT Name FROM clanmembers WHERE Name='%s' LIMIT 1",params);//Selecting the name from the table.
    mysql_query(String);
    mysql_store_result();//Storing the result.
    if(mysql_num_rows() == 0)return (mysql_free_result() && SendClientMessage(playerid,-1,"That name was not found in the table."));//Freeing the result, and giving an error that the name entered is not in the table.
    mysql_free_result();//Freeing the result.
    format(String,60,"DELETE FROM clanmembers WHERE Name='%s'",params);//If the name was found, then delete it.
    mysql_query(String);
    format(String,100,"You've removed %s from the clan.",params);
    SendClientMessage(playerid,-1,String);
    return 1;
}

new namevar[MAX_PLAYER_NAME];
new escapename[MAX_PLAYER_NAME];
// Replace GetName To GetPlayerName