Update table lookup - tsql

Question

I have a temp table (#WorkTable) which looks like the following:
InstrID CountryName CreditRating
1 UK AA
2 UK Unclassified
3 South Africa A
4 South Africa A
5 South Africa Unclassified
What I want to be able to do is update this table where column CreditRating is 'Unclassified' with its actual credit rating. So in the example above the UK unclassified would become 'AA' and the South African one would become 'A'.
I'm unsure of the coding for this, any help would be greatly appreciated.

Answer 1

The sql script below will update any unclassified to the 'actual' credit ratings. I hope this helps.
CREATE TABLE #WorkTable
(
InstrID INT,
CountryName VARCHAR(50),
CreditRating VARCHAR(20)
)
INSERT INTO #WorkTable VALUES ( 1, 'UK','AA');
INSERT INTO #WorkTable VALUES ( 2, 'UK','Unclassified');
INSERT INTO #WorkTable VALUES ( 3, 'South Africa','A');
INSERT INTO #WorkTable VALUES ( 4, 'South Africa','A');
INSERT INTO #WorkTable VALUES ( 5, 'South Africa','Unclassified');
WITH cteUnclassified
AS
(
SELECT InstrID,
CountryName,
CeditRating
FROM #WorkTable
WHERE CreditRating != 'Unclassified'
)
UPDATE #WorkTable
SET CreditRating = u.CreditRating
FROM #WorkTable wt
INNER JOIN cteUnclassified u
ON wt.CountryName = u.CountryName
WHERE wt.CreditRating = 'Unclassified'
SELECT *
FROM #WorkTable
Result of the query below:
InstrID CountryName CreditRating
1 UK AA
2 UK AA
3 South Africa A
4 South Africa A
5 South Africa A

Answer 2

I think This example would help you.
String sql = "update table_name set CreditRating = (select unique CreditRating from table_name where CountryName = ? and CreditRating != 'classifie...') where CountryName = ? and CreditRating = 'classifie...'";
Here you can pass the countryName as a paramaeter.

Answer 3

You seem new to SQL. What you need to do is "join" the table to the lookup values. You can find a lot of help on basics of SQL in a lot of places, but if you need a quick solution, try the following:
If you havea seperate table with countries and credit ratings, (I have assumed the name of that table is Rating, and the country names and rating match.)
update #WorkTable
Set w.Creditrating = r.CreditRating
from #WorkTable w join Rating r on w.CountryName=r.CountryName
where w.CreditRating='Unclassified'
On the other hand, if no seperate table exists, and you want to update the unclassified values based on the same temp table, then you need to assume that there is some entry with a CreditRating for that country in the table already (which, in the case you posted, there is.) It also needs for there to be only one CreditRating per country. In this case, the following should work:
update #WorkTable
Set w.Creditrating = w2.CreditRating
from #WorkTable w join
(Select distinct CountryName, CreditRating from #WorkTable where CreditRating<>'Unclassified') w2
on w.CountryName=w2.CountryName
where w.CreditRating='Unclassified'
This uses the table itself to find the values, by looking at the table twice - once as the table to update, where the last line restricts what is updated to only the unclassified items, and once as a source table, where only classified ratings are used. Please leave a comment with more details if this doesn't work for you.