Need help tuning join in slow query

Question

Hi all,
I have the following issue to tune the below join condition in my query below:
SELECT PO.COMPANY,
PO.UPDATE_DATE,
PO.EXTENDED_AMT,
PO.LOCATION,
ICLOCATION.R_NAME AS LOCATION_DESC,
PO.VENDOR,
AP.VENDOR_VNAME,
MAJOR.DESCRIPTION AS MAJOR_DESC,
MINOR.DESCRIPTION AS MINOR_DESC,
CASE po.purch_majcl
WHEN ' '
THEN 'NONE'
ELSE po.purch_majcl
END AS PURCH_MAJ,
CASE po.purch_min
WHEN ' '
THEN 'NONE'
ELSE po.purch_min
END AS PURCH_MIN,
CASE po.manuf_code
WHEN ' '
THEN 'NO MFG'
ELSE po.manuf_code
END AS MANUF_CODE,
CASE po.manuf_nbr
WHEN ' '
THEN 'NONE'
ELSE po.manuf_nbr
END AS MANUF_NBR,
CASE po.manuf_division
WHEN ' '
THEN 'NONE'
ELSE po.manuf_division
END AS MANUF_DIV,
CASE po.agreement_ref
WHEN ' '
THEN 'NONE'
ELSE PO.AGREEMENT_REF
END AS AGRMT_REF,
/* ITEMLOC IS REQUIRED TO GET TO ICCACATEGORY */
CASE po.item_type
WHEN 'I'
THEN ICCATEGORY.INV_ACCT_UNIT
ELSE MMDIST.ACCT_UNIT
END AS ACCT_UNIT,
CASE po.item_type
WHEN 'I'
THEN ICCATEGORY.GL_CATEGORY
ELSE to_char(MMDIST.ACCOUNT)
END AS ACCOUNT,
/* ITEMLOC IS REQUIRED TO GET TO ICCACATEGORY */
PO.ITEM_TYPE,
PO.ITEM,
PO.DESCRIPTION AS ITEM_DESC,
PO.ENT_REC_UOM,
PO.ENT_RUOM_MULT,
PO.ENT_REC_QTY,
PO.ORIG_UNIT_CST,
PO.MATCH_UNIT_CST,
PO.PO_NUMBER,
PO.PO_LINE_NBR,
PO.QTY_TO_PROC,
PURCHORDER.PO_DATE,
PURCHORDER.BUYER_CODE,
BUYER.R_NAME AS BUYER_NAME
FROM LAW.PURCHORDER, LAWS81.BUYER,
LAW.ICLOCATION, LAW.APVENMAST,
LAW.PO LEFT JOIN LAW.MMDIST
ON (PO.COMPANY = MMDIST.COMPANY
AND PO.LOCATION = MMDIST.LOCATION
AND PO.PO_NUMBER = MMDIST.DOC_NUMBER
AND PO.PO_RELEASE = MMDIST.DOC_NBR_NUM
AND PO.PO_CODE = MMDIST.PO_CODE
AND PO.PO_LINE_NBR = MMDIST.LINE_NBR
AND MMDIST.SYSTEM_CD = 'PO'
AND MMDIST.DOC_TYPE = 'PT'
AND MMDIST.COMPONENT_SEQ = 0
AND MMDIST.AOC_CODE = ' ')
/* 1st JOIN TO ITEMLOC */
LEFT JOIN LAW.ITEMLOC
ON PO.COMPANY = ITEMLOC.COMPANY
AND PO.LOCATION = ITEMLOC.LOCATION
AND PO.ITEM = ITEMLOC.ITEM,
/* 2nd JOIN from ITEMLOC to ICCATEGORY */
/* It should use the ITEMLOC join from above */
/* creating cartesian product with itemloc */
LAW.ITEMLOC LEFT JOIN LAW.ICCATEGORY
ON ITEMLOC.COMPANY = ICCATEGORY.COMPANY
AND ITEMLOC.LOCATION = ICCATEGORY.LOCATION
AND ITEMLOC.GL_CATEGORY = ICCATEGORY.GL_CATEGORY,
/* need to get to ICCATEGORY table using 2nd JOIN condition above */
LAW.PO LEFT JOIN LAW.MAJOR
ON PO.PURCH_MAJ = MAJOR.MAJOR_CLASS
AND MAJOR.CLASS_TYPE = 'P'
LEFT JOIN LAW.MINOR
ON PO.PURCH_MAJCL = MINOR.MAJOR_CLASS
AND PO.PURCH_MINCL = MINOR.MINOR_CLASS
AND MINOR.CLASS_TYPE = 'P'
WHERE PO.COMPANY = PO.COMPANY
AND PO.PO_NUMBER = PO.PO_NUMBER
AND PO.PO_RELEASE = PO.PO_RELEASE
AND PO.PO_CODE = PO.PO_CODE
AND PO.PO_LINE_NBR = PO.LINE_NBR
AND PO.COMPANY = ICLOCATION.COMPANY
AND PO.LOCATION = ICLOCATION.LOCATION
AND PO.VENDOR = APVENMAST.VENDOR
AND PO.COMPANY = PURCHORDER.COMPANY
AND PO.PO_CODE = PURCHORDER.PO_CODE
AND PO.PO_NUMBER = PURCHORDER.PO_NUMBER
AND PO.PO_RELEASE = PURCHORDER.PO_RELEASE
AND PURCHORDER.BUYER_CODE = BUYER.BUYER_CODE
AND PO.R_STATUS = 1
AND PO.ENT_REC_QTY > 0
This query runs very slow and we cannot change the code to add or modify indexes. We need to join the 2nd table to the third table with optimized performance. How can I tune this slow running query with the best join conditions?
Thanks

Answer 1

I want to join the OS_LOCN_CURR_STK table with the
OT_PO_ITEM table , such that all items in
OS_LOCN_CURR_STK are displayed.
If you want all items in OS_LOCN_CURR_STK to be returned, use an OUTER JOIN on the columns joining the 2 tables.