Jeg tror på en UPDATE FROM
med en JOIN
vil hjælpe:
MS SQL
UPDATE
Sales_Import
SET
Sales_Import.AccountNumber = RAN.AccountNumber
FROM
Sales_Import SI
INNER JOIN
RetrieveAccountNumber RAN
ON
SI.LeadID = RAN.LeadID;
MySQL og MariaDB
UPDATE
Sales_Import SI,
RetrieveAccountNumber RAN
SET
SI.AccountNumber = RAN.AccountNumber
WHERE
SI.LeadID = RAN.LeadID;