sp_who (Transact-SQL MetaData) Definition

Please note: that the following source code is provided and copyrighted by Microsoft and is for educational purpose only.
The meta data is from an SQL 2012 Server.

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Definition:

sys.sp_who(nvarchar @loginame)

MetaData:

 create procedure sys.sp_who  -- - 1995/11/28 15:48  
       @loginame sysname = NULL -- or 'active'  
as  
  
declare     @spidlow    int,  
         @spidhigh    int,  
         @spid        int,  
         @sid        varbinary(85)  
  
select     @spidlow    =     0  
        ,@spidhigh    = 32767  
  
  
if (    @loginame is not NULL  
   AND    upper(@loginame collate Latin1_General_CI_AS) = 'ACTIVE'  
   )  
    begin  
  
    select spid , ecid, status  
              ,loginame=rtrim(loginame)  
          ,hostname ,blk=convert(char(5),blocked)  
          ,dbname = case  
                        when dbid = 0 then null  
                        when dbid <> 0 then db_name(dbid)  
                    end  
          ,cmd  
          ,request_id  
    from  sys.sysprocesses_ex  
    where spid >= @spidlow and spid <= @spidhigh AND  
          upper(cmd) <> 'AWAITING COMMAND'  
  
    return (0)  
    end  
  
if (@loginame is not NULL  
   AND    upper(@loginame collate Latin1_General_CI_AS) <> 'ACTIVE'  
   )  
begin  
    if (@loginame like '[0-9]%')    --  is a spid.  
    begin  
        select @spid = convert(int, @loginame)  
        select spid, ecid, status,  
               loginame=rtrim(loginame),  
               hostname,blk = convert(char(5),blocked),  
               dbname = case  
                            when dbid = 0 then null  
                            when dbid <> 0 then db_name(dbid)  
                        end  
              ,cmd  
              ,request_id  
        from  sys.sysprocesses_ex  
        where spid = @spid  
    end  
    else  
    begin  
        select @sid = suser_sid(@loginame)  
        if (@sid is null)  
        begin  
            raiserror(15007,-1,-1,@loginame)  
            return (1)  
        end  
        select spid, ecid, status,  
               loginame=rtrim(loginame),  
               hostname ,blk=convert(char(5),blocked),  
               dbname = case  
                            when dbid = 0 then null  
                            when dbid <> 0 then db_name(dbid)  
                        end  
               ,cmd  
               ,request_id  
        from  sys.sysprocesses_ex  
        where sid = @sid  
    end  
    return (0)  
end  
  
  
--  loginame arg is null  
select spid,  
       ecid,  
       status,  
       loginame=rtrim(loginame),  
       hostname,  
       blk=convert(char(5),blocked),  
       dbname = case  
                    when dbid = 0 then null  
                    when dbid <> 0 then db_name(dbid)  
                end  
       ,cmd  
       ,request_id  
from  sys.sysprocesses_ex  
where spid >= @spidlow and spid <= @spidhigh  
  
return (0) --  sp_who