How to derive Supporting reference

Hi  All

i wanted to derive supporting reference for GL lines for that i am using following query . But it seems it is taking more time , Please help me in figuring out if any thing is missing . Thanks in advance .

SELECT

      xfurts.ae_header_id,

      xfurts.ae_line_num,

      DECODE(xadv.grouping_order,1,xala.ac1,2,xala.ac2,3,xala.ac3,4,xala.ac4,5,xala.ac5)  unique_trans

   FROM

      xlg_fah_usd_rep_trans_stg xfurts, -- Custom table that extract ae_header and line number from base table , Now deriving supporting reference for those ae_line number

      xla_ae_line_acs xala,