Query Simplification for better execution Select a.item_no,
       a.item_type,
       a.item_group,
       a.uom_group,
       a.unit_price,
       c.service_category,
       c.item_no,
       b.manufacturer,
       b.issue_method,
       b.item_no,
       d.preferred_vender,
       d.mfr_catlog_no,
       d.purchasing_uom,
       d.items_per_purchase_unit,
       d.quantity_per_package,
       d.item_no,
       e.sales_uom_name,
       e.item_per_sales_unit,
       e.package_uom_name,
       e.quanti_per_package,
       e.item_no
  from Item_Master_Details a, 
       Item_Master_General_Material b, 
       Item_Master_General_Service c, 
       Item_Master_Purchasing_Data d, 
       Item_Master_Sales_Data e
 where a.item_no = b.item_no 
   and b.item_no = c.item_no 
   and c.item_no = d.item_no 
   and d.item_no = e.item_no;


I want to simplify this query..because it gets more time to execute in database.
Other than changing your query so that you are using a JOIN when referencing your tables there is not much that can be done to simplify the query itself as it is pretty basic. Here is your query rewritten to use a JOIN:

Select a.item_no,
       a.item_type,
       a.item_group,
       a.uom_group,
       a.unit_price,
       c.service_category,
       c.item_no,
       b.manufacturer,
       b.issue_method,
       b.item_no,
       d.preferred_vender,
       d.mfr_catlog_no,
       d.purchasing_uom,
       d.items_per_purchase_unit,
       d.quantity_per_package,
       d.item_no,
       e.sales_uom_name,
       e.item_per_sales_unit,
       e.package_uom_name,
       e.quanti_per_package,
       e.item_no
  from Item_Master_Details a 
  join Item_Master_General_Material b 
    on a.item_no = b.item_no
  join Item_Master_General_Service c 
    on b.item_no = c.item_no 
  join Item_Master_Purchasing_Data d 
    on c.item_no = d.item_no 
  join Item_Master_Sales_Data e 
    on d.item_no = e.item_no;


If it is still running slow then you might want to consider an indexing strategy, materialized views or even creating a de-normalized table to contain the data that you require.