Merging Inventory Data With Other Data

Dear Experts,

I have a requirement where in i am trying to combine Inventory Data with data from other datasource (0CO_PC_ACT_05).

I have designed the Bex query from both the sources. Now i have tried to merge the data at BO level by merging dimesions

plant and material. It works fine for small data set  but there is performance issue as we have huge inventory data of more than 15 years.

Kindly suggest me the other methods through which i can merge the data.

Thanks ,

Sumit