SQL - More efficient way instead of using a cursor - sql

Question

-- Declare the table we are interested in reverting.
DECLARE #table_name VARCHAR(1000)
SET #table_name = 'tblCustomers' -- change this
-- Declare cursor and use the select statement (the one we want to loop through).
DECLARE customer_cursor CURSOR FOR
SELECT C.CustomerId
FROM tblCustomers C
WHERE ModifiedBy like '%crm%'
ORDER BY C.CustomerId DESC
-- Open the cursor and copy the columns into the original_consumer variable.
DECLARE #customer_id INT
OPEN customer_cursor
FETCH NEXT FROM customer_cursor
INTO #customer_id
-- Now loop through the old consumer id's and update their corresponding purchase and refunds records.
WHILE ##FETCH_STATUS = 0
BEGIN
IF EXISTS ( SELECT TOP 1 UserName
FROM tblAudit
WHERE TableName = #table_name
AND TableId IN (
SELECT CONVERT(VARCHAR, CustomerId)
FROM tblCustomers -- change this
WHERE CustomerId = #customer_id
)
AND UserName != 'crmuser'
ORDER BY TransactionDate DESC)
BEGIN
UPDATE tblCustomers
SET ModifiedBy = (SELECT TOP 1 UserName
FROM tblAudit
WHERE TableName = #table_name
AND TableId IN (
SELECT CONVERT(VARCHAR, CustomerId)
FROM tblCustomers -- change this
WHERE CustomerId = #customer_id
)
AND UserName != 'crmuser'
ORDER BY TransactionDate DESC),
ModifiedDate = (SELECT TOP 1 TransactionDate
FROM tblAudit
WHERE TableName = #table_name
AND TableId IN (
SELECT CONVERT(VARCHAR, CustomerId)
FROM tblCustomers -- change this
WHERE CustomerId = #customer_id
)
AND UserName != 'crmuser'
ORDER BY TransactionDate DESC)
WHERE CustomerId = #customer_id
END
FETCH NEXT FROM customer_cursor INTO #customer_id
END
-- Finally close and deallocate the cursor to stop memory leakage.
CLOSE customer_cursor
DEALLOCATE customer_cursor

Answer 1

This looks like it might work:
UPDATE tblCustomers
SET ModifiedBy = a.UserName,
ModofiedDate = amax.LatestChangeDate
from tblCustomers t
inner join -- get the latest transaction_date for each customer
(
select customerId, max(transaction_date) LatestChangeDate
from tblAudit
where TableName = #table_name
) amax on amax.customerId = t.customer_id
inner join -- get the details of changes for customer and latest date
(
select CustomerId, UserName, transaction_date
from tblAudit
where table_name = #table_name
) a on a.customerId = t.customerId and a.transaction_date = amax.LatestChangeDate
WHERE t.CustomerId = #customer_id
);
(I might have some of the column names wrong.)

Answer 2

BEGIN TRAN
SELECT COUNT(*)
FROM tblInvoices
WHERE ModifiedBy = 'DataImporterUser'
;WITH cte AS
(
SELECT TableId,
TransactionDate,
UserName,
TransactionDetail,
ROW_NUMBER() OVER (PARTITION BY TableId ORDER BY TransactionDate DESC) AS rn
FROM tblAudit
WHERE TableName = 'tblInvoices'
AND UserName <> 'DataImporterUser'
)
UPDATE C
SET C.ModifiedBy = cte.UserName,
C.ModifiedDate = cte.TransactionDate
FROM tblInvoices AS C
INNER JOIN cte
ON cte.TableId = C.InvoiceId
WHERE rn = 1
SELECT COUNT(*)
FROM tblEvents
WHERE ModifiedBy = 'DataImporterUser'
ROLLBACK