How to copy a foreign key constrained table to another database? - sql-server

Question

I'm trying to replace gibberish data on my development server (recovering it from the production server).
I first tried using SSMS's "import data" task, but encountered an error saying: "Cannot truncate a table with a foreign key constraint" therefore I resolved to do the following:
Create a new temp copy of the table on the development server (to avoid accessing it from the production database).
Write an update script.
This is my script:
DECLARE #IdToCopy INT;
DECLARE #cnt INT;
SET #IdToCopy = 1
WHILE #IdToCopy <= 55
BEGIN
UPDATE DocumentTypes
SET Name = DocumentTypesTemp.Name
FROM DocumentTypesTemp
WHERE DocumentTypesTemp.DocumentTypeId = #IdToCopy;
SET #IdToCopy += 1;
END;
I expected it to update the table to have the same values, but the only value was that of the last row from the copying table.

Answer 1

I expected it to update the table to have the same values, but the
only value was that of the last row from the copying table.
In each iteration of while loop, your entire DocumentTypes table is getting updated. This is the reason, you see only last record name appearing in the entire table, you have to join the source and destination table based on the id.
UPDATE dest
SET dest.NAME = src.NAME
FROM documenttypes dest
INNER JOIN documenttypestemp src
ON src.documenttypeid = dest.documenttypeid
Above query will update the name from destination table to source table with matching documenttypeid in a single query.
Note: You don't need a while loop to update the name from source to destination.

Answer 2

I fixed my script using the following:
DECLARE #IdToCopy INT;
DECLARE #cnt INT;
DECLARE #NameToCopy varchar(256);
SET #IdToCopy=1
SELECT #cnt=COUNT(*) FROM DocumentTypesTemp;
WHILE #IdToCopy <= #cnt
BEGIN
SELECT #NameToCopy=Name
FROM DocumentTypesTemp
WHERE DocumentTypesTemp.DocumentTypeId=#IdToCopy;
UPDATE DocumentTypes
SET Name=#NameToCopy
WHERE DocumentTypes.DocumentTypeId=#IdToCopy;
SET #IdToCopy += 1;
END;