Rewriting SQL query to simplify logic - sql

Question

I'm quite a newbie in optimizing queries.. it would be a first for me to handle other persons query and optimize it to improve performance. Can you kindly give me advice on which part of the query could I simplify in order to improve its performance....
CREATE FUNCTION SALES
(#SUPPLIERCODE VARCHAR(15),
#BATCHID VARCHAR(50))
RETURNS
#STOCKDETAILS TABLE([ID] CHAR(1),
[BATCH RECEIVEDATE] DATETIME,
SUPPLIERCODE VARCHAR(15),
[NOW - RECEVEDATE] INT,
[DUEDATE] VARCHAR(50)
)
AS
BEGIN
DECLARE #RECEIVEDATE DATETIME,
#SUPPLIERCODE1 VARCHAR(15)
SELECT TOP 1
#RECEIVEDATE = O.ReceivedDate,
#SUPPLIERCODE1 = A.SUPPLIERCODE
FROM
TRANSACT.dbo.FIELDS A WITH(NOLOCK)
INNER JOIN
TRANSACT.dbo.DELIV O WITH(NOLOCK) ON O.BATCHID = A.BATCHID
DECLARE #ID1 TABLE(SUPPLIERCODE VARCHAR(50))
INSERT INTO #ID1
SELECT P.SUPPLIERCODE
FROM
(SELECT
[SUPPLIERCODE] = SUPPLIERCODE,
[TOTAL] = ISNULL(SUM(ITEMPRICE + (ITEMPRICE * .12)), 0)
FROM TRANSACT.dbo.ProviderDiscount WITH(NOLOCK)
WHERE ACQUIREDDATE <> '1900-01-01 00:00:00.000'
AND SUPPLIERCODE = #SUPPLIERCODE1
GROUP BY SUPPLIERCODE) P
WHERE P.TOTAL <> 0
DECLARE #ID TABLE ([BATCH RECEIVEDATE] DATETIME,
SUPPLIERCODE VARCHAR(15),
ACQUIREDDATE DATETIME,
Coverage VARCHAR(20),
CoverageItem VARCHAR(10),
[NOW - RECEVEDATE] INT,
DiscTerm1 INT, DiscTerm2 INT,
DiscTerm3 INT, DiscTerm4 INT,
DiscTerm5 INT,
[NEW ACQUIREDDATE] VARCHAR(50)
)
INSERT INTO #ID
SELECT DISTINCT
[BATCH RECEIVEDATE] = #RECEIVEDATE,
B.SUPPLIERCODE,
B.ACQUIREDDATE,
B.Coverage,
B.CoverageItem,
[NOW - RECEVEDATE] = DATEDIFF(DAY,#RECEIVEDATE,GETDATE()),
B.DiscTerm1, B.DiscTerm2, B.DiscTerm3,
B.DiscTerm4, B.DiscTerm5,
[NEW ACQUIREDDATE] = TRANSACT.dbo.fxnGetIDNewACQUIREDDATE(B.DiscTerm1, B.DiscTerm2, B.DiscTerm3, B.DiscTerm4, B.DiscTerm5, #RECEIVEDATE)
FROM
TRANSACT.dbo.ProviderDiscount B WITH(NOLOCK)
INNER JOIN
(SELECT
[ACQUIREDDATE] = MAX(ACQUIREDDATE),
[REOD] = MAX(REOD)
FROM
TRANSACT.dbo.ProviderDiscount B2 WITH(NOLOCK)
INNER JOIN
#ID1 B1 ON B1.SUPPLIERCODE = B2.SUPPLIERCODE
WHERE
B2.Coverage = #CLAIMTYPE
AND B2.ACQUIREDDATE < #RECEIVEDATE) B3 ON B3.REOD = B.REOD
INSERT INTO #STOCKDETAILS
SELECT DISTINCT
[ID] = 'Y',
[BATCH RECEIVEDATE],
SUPPLIERCODE,
[NOW - RECEVEDATE],
[DUEDATE] = MIN([NEW ACQUIREDDATE])
FROM
#ID
WHERE
ISNULL([NEW ACQUIREDDATE],'NONE') <> 'NONE'
GROUP BY
[BATCH RECEIVEDATE], SUPPLIERCODE, [NOW - RECEVEDATE]
RETURN
END

Answer 1

Well, here's one thing you can do.
DECLARE #ID1 TABLE(SUPPLIERCODE VARCHAR(50))
INSERT INTO #ID1
SELECT P.SUPPLIERCODE
FROM
(
SELECT
[SUPPLIERCODE] = SUPPLIERCODE,
[TOTAL] = ISNULL(SUM(ITEMPRICE+(ITEMPRICE*.12)),0)
FROM TRANSACT.dbo.ProviderDiscount WITH(NOLOCK)
WHERE ACQUIREDDATE <> '1900-01-01 00:00:00.000'
AND SUPPLIERCODE = #SUPPLIERCODE1
GROUP BY SUPPLIERCODE
) P
WHERE P.TOTAL <> 0
Can be rewritten stripped of lots of extra. Maybe even more than I do here:
DECLARE #ID1 TABLE(SUPPLIERCODE VARCHAR(50))
INSERT INTO #ID1
SELECT SUPPLIERCODE
FROM TRANSACT.dbo.ProviderDiscount WITH(NOLOCK)
WHERE ACQUIREDDATE <> '1900-01-01 00:00:00.000'
AND SUPPLIERCODE = #SUPPLIERCODE1
GROUP BY SUPPLIERCODE
HAVING ISNULL(SUM(ITEMPRICE),0) <> 0
This almost looks like test question for refactoring SQL.