Report query taking too long.....

Hi all,

Issue with the following query. The following query sometimes run smoothly and fetch data in just seconds.

But sometimes the same query takes more than 30 to 40 min to execute.

Kindly, suggest about this issue. What would be possible issues causing this query to mis-behave.

select to_number(FFV.ATTRIBUTE1) ,

       aps.VENDOR_ID,

       null,

       gjh.DEFAULT_EFFECTIVE_DATE,

       null,

       GCC.SEGMENT6  PROGRAM,

       gjh.DOC_SEQUENCE_VALUE REF_NO,

       gjl.DESCRIPTION,

       SUM(gjl.ENTERED_CR) CREDIT,

       SUM(gjl.ENTERED_DR)  DEBIT

from gl_je_lines gjl,

     gl_je_headers gjh,

     gl_code_combinations gcc,

     ap_suppliers aps,

(SELECT  PAPF.PARTY_ID