Could use advice in making my query smarter - sql

Question

Hi Guys I have the following query but the unions make it quite heavy so could anyone help in fixing my query.
There are 3 scenarios.
1. pack_no = pack of an item (inside packitem)
2. item = item inside pack (inside packitem)
3. item = doesn't have pack (inside item_master)
SELECT DISTINCT item, loc FROM
(SELECT e.pack_no item, g.store loc
FROM dc_store_ranging a
JOIN store g
ON g.store_name_secondary = CAST(a.loc AS VARCHAR2(150 BYTE)) AND
g.store_close_date >= SYSDATE
LEFT JOIN dc_pim_export_vert b
ON a.dpac = b.dpac AND b.artikel_type_LMS NOT IN ('S','V')
LEFT JOIN dc_ccn190_sid_vtb c ON a.dpac = c.dpac
JOIN item_master d
ON (b.item = d.item OR c.item = d.item) AND d.status = 'A'
LEFT JOIN packitem e
ON (b.item = e.pack_no or c.item = e.pack_no) AND d.item = e.pack_no
WHERE d.item NOT IN
(SELECT f.item
FROM item_attributes f
WHERE f.sh_store_order_unit = 'N' AND f.sh_trade_unit = 'Y')
UNION
SELECT e.item, g.store loc
FROM dc_store_ranging a
JOIN store g
ON g.store_name_secondary = CAST(a.loc AS VARCHAR2(150 BYTE)) AND
g.store_close_date >= SYSDATE
LEFT JOIN dc_pim_export_vert b
ON a.dpac = b.dpac AND b.artikel_type_LMS NOT IN ('S','V')
LEFT JOIN dc_ccn190_sid_vtb c ON a.dpac = c.dpac
JOIN item_master d
ON (b.item = d.item OR c.item = d.item) AND d.status = 'A'
LEFT JOIN packitem e
ON (b.item = e.pack_no or c.item = e.pack_no)
WHERE e.item NOT IN
(SELECT f.item
FROM item_attributes f
WHERE f.sh_store_order_unit = 'N' AND f.sh_trade_unit = 'Y')
UNION
SELECT d.item, g.store loc
FROM dc_store_ranging a
JOIN store g
ON g.store_name_secondary = CAST(a.loc AS VARCHAR2(150 BYTE)) AND
g.store_close_date >= SYSDATE
LEFT JOIN dc_pim_export_vert b
ON a.dpac = b.dpac AND b.artikel_type_LMS NOT IN ('S','V')
LEFT JOIN dc_ccn190_sid_vtb c ON a.dpac = c.dpac
JOIN item_master d
ON (b.item = d.item OR c.item = d.item) AND d.status = 'A'
WHERE d.item NOT IN
(SELECT f.item
FROM item_attributes f
WHERE f.sh_store_order_unit = 'N' and f.sh_trade_unit = 'Y')
);

Answer 1

The simplest way to improve the performance of the query would be to change the UNIONs to UNION ALLs - that way, the query only has to eliminate duplicates once.
However, it should be possible to simplify this query to:
WITH CTE AS
(SELECT d.item d_item, e.item e_item, e.pack_no e_pack_no, g.store loc
FROM dc_store_ranging a
JOIN store g
ON g.store_name_secondary = CAST(a.loc AS VARCHAR2(150 BYTE)) AND
g.store_close_date >= SYSDATE
LEFT JOIN dc_pim_export_vert b
ON a.dpac = b.dpac AND b.artikel_type_LMS NOT IN ('S','V')
LEFT JOIN dc_ccn190_sid_vtb c ON a.dpac = c.dpac
JOIN item_master d
ON (b.item = d.item OR c.item = d.item) AND d.status = 'A'
LEFT JOIN packitem e
ON (b.item = e.pack_no or c.item = e.pack_no)
)
SELECT DISTINCT item, loc FROM
(--SELECT e_pack_no item, loc FROM CTE WHERE d_item = e_pack_no UNION ALL -- this select is a subset of the third select
SELECT e_item item, loc FROM CTE UNION ALL
SELECT d_item item, loc FROM CTE) uc
WHERE uc.item NOT IN
(SELECT f.item
FROM item_attributes f
WHERE f.sh_store_order_unit = 'N' and f.sh_trade_unit = 'Y')