Using Variable as part of column name in Dynamic SQL - sql

Question

I am trying to use a variable as part of a column name in a dynamic SQL statement.
I have 4 columns that are called Player1Action, Player2Action, Player3Action and Player4Action.
Depending on the varaible #CurrentPlayerId, I want to update the relevant player column with some data.
So for example, if CurrentPlayerId contains 1, then update column Player1Action.
I realise I could achieve this with a series of IF statements, but I would like to do it in a cleaner manner.
I have the following code, but I think my escaping is causing issues. I have re-written this a view times but I don't seem to be able to get it to work.
DECLARE
#CurrentPlayerId INT,
#CurrentPlayerBetAmount nvarchar(MAX),
#stmt nvarchar(MAX);
SET #CurrentPlayerId = 1
SET #CurrentPlayerBetAmount = 100
SET #stmt = N'UPDATE HandCurrent SET ''Player'' ''+'' #CurrentPlayerId ''+'' ''Action'' = 1 '','' ''Player'' ''+'' #CurrentPlayerId ''+'' ''ActionSize'' = #CurrentPlayerBetAmount'
EXECUTE sp_executesql #stmt
If I run this as a select I get the following returned.
UPDATE HandCurrent SET 'Player' '+' #CurrentPlayerId '+' 'Action' = 1 ',' 'Player' '+' #CurrentPlayerId '+' 'ActionSize' = #CurrentPlayerBetAmount

Answer 1

DECLARE
#CurrentPlayerId INT,
#CurrentPlayerBetAmount INT,
#stmt nvarchar(MAX);
SET #CurrentPlayerId = 1
SET #CurrentPlayerBetAmount = 100
SET #stmt = N'UPDATE HandCurrent SET
Player' + CAST(#CurrentPlayerId AS NVARCHAR(10)) + 'Action = 1,
Player' + CAST(#CurrentPlayerId AS NVARCHAR(10)) + 'ActionSize = '
+ CAST(#CurrentPlayerBetAmount AS NVARCHAR(10))
EXECUTE sp_executesql #stmt
Juan Carlos had it right only issue is datatypes of variables #CurrentPlayerId is an INT so you would need to cast it to NVARCHAR() https://www.mssqltips.com/sqlservertip/3014/concatenation-of-different-sql-server-data-types/.
To be consistent you should have declared #CurrentPlayerBetAmount as INT as well. If you do then you need to cast it too.
However, you could also simply DECLARE both as NVARCAHR(MAX) and then single quote the value when setting it such as:
DECLARE
#CurrentPlayerId NVARCHAR(MAX),
#CurrentPlayerBetAmount NVARCHAR(MAX),
#stmt nvarchar(MAX);
SET #CurrentPlayerId = '1'
SET #CurrentPlayerBetAmount = '100'
SET #stmt = N'UPDATE HandCurrent SET
Player' + #CurrentPlayerId + 'Action = 1,
Player' + #CurrentPlayerId + 'ActionSize = ' + #CurrentPlayerBetAmount
EXECUTE sp_executesql #stmt
Or My preference if you are going to change a record anyway would be just to do the update statement if you have 4 columns. You could also think of nth Normalizing and making the columns Rows....
DECLARE #CurrentPlayerId INT = 1
DECLARE #CurrentPlayerBetAmount INT = 100
UPDATE HandCurrent
Player1Action = CASE WHEN #CurrentPlayerId = 1 THEN 1 ELSE PlayerAction1 END
,Player1ActionSize = CASE WHEN #CurrentPlayerId = 1 THEN #CurrentPlayerBetAmount ELSE Player1ActionSize END
,Player2Action = CASE WHEN #CurrentPlayerId = 2 THEN 1 ELSE PlayerAction2 END
,Player2ActionSize = CASE WHEN #CurrentPlayerId = 2 THEN #CurrentPlayerBetAmount ELSE Player2ActionSize END
,Player3Action = CASE WHEN #CurrentPlayerId = 3 THEN 1 ELSE PlayerAction3 END
,Player3ActionSize = CASE WHEN #CurrentPlayerId = 3 THEN #CurrentPlayerBetAmount ELSE Player3ActionSize END
,Player4Action = CASE WHEN #CurrentPlayerId = 4 THEN 1 ELSE PlayerAction4 END
,Player4ActionSize = CASE WHEN #CurrentPlayerId = 4 THEN #CurrentPlayerBetAmount ELSE Player4ActionSize END
WHERE
????
Note you are actually updating the entire table is that what you desire?

Answer 2

dont quote the variables.
SET #stmt = N'UPDATE HandCurrent SET
Player' + #CurrentPlayerId + 'Action = 1,
Player' + #CurrentPlayerId + 'ActionSize = ' + #CurrentPlayerBetAmount

Answer 3

Speaking of cleanest way to do this, IMHO the best approach is to use sp_executesql with parameters, implying the #CurrentPlayerId and #CurrentPlayerBetAmount are input parameters of the given code:
Declare #sql nvarchar(256)
, #sql1 nvarchar(256) = N'update HandCurrent
Set Player1Action =#value,
Player1ActionSize =#size'
, #sql2 nvarchar(256) = N'update HandCurrent
Set Player2Action =#value,
Player2ActionSize =#size'
, #params nvarchar (128)
, #CurrentPlayerId int
;
Select #sql = case #CurrentPlayerId when 1 then #sql1 when 2 then #sql2 else '' end;
If #sql <> '' begin
set #params = N'#value int, #size int';
execute sp_executesql #sql, #params,
#value =1,
#size = #CurrentPlayerBetAmount
;
End