Case when in Select, Left Join and Group By - sql

Question

how can i archive the following?
If #chk = 0 then include 4th Column in result else keep only 3 Columns,
and if 4th Column is selected then Left join is needed for that 4th column,
and include that 4th column in group by
DECLARE #chk AS INT= 0;
SELECT a.Ledgerid,
b.LedgerCity,
CASE WHEN #chk = 0 THEN SUM(a.TotalAmount) ELSE SUM(a.NetAmount) END,
CASE WHEN #chk = 0 THEN c.ledgername END (is it possilbe to completly do not have this column if #chk <> 0)
FROM ExpenseMaster A
LEFT JOIN LedgerAddress AS B ON A.LedgerID = B.LedgerID
LEFT JOIN LedgerMaster AS C ON A.LedgerID = C.LedgerID --This left join is required only if #chk=0, same logic is there in above select statement
GROUP BY A.LedgerID,
B.LedgerCity;
C.LedgerName; -- this 3rd group required only if #chk=0
some posts suggested how to use case when in Group by. I tried "group by case when #chk=0 then a.Ledgerid,b.Ledgercity,c.LedgerName else a.Ledgerid,b.Ledgercity END; but this did not work

Answer 1

Use IF .. ELSE block
IF #chk = 0
BEGIN
SELECT a.Ledgerid,
b.LedgerCity,
CASE WHEN #chk = 0 THEN SUM(a.TotalAmount) ELSE SUM(a.NetAmount) END,
CASE WHEN #chk = 0 THEN c.ledgername END
FROM ExpenseMaster A
LEFT JOIN LedgerAddress AS B ON A.LedgerID = B.LedgerID
LEFT JOIN LedgerMaster AS C ON A.LedgerID = C.LedgerID --This left join is required only if #chk=0, same logic is there in above select statement
GROUP BY A.LedgerID, B.LedgerCity, C.LedgerName;
END
ELSE
BEGIN
SELECT a.Ledgerid,
b.LedgerCity,
CASE WHEN #chk = 0 THEN SUM(a.TotalAmount) ELSE SUM(a.NetAmount) END
FROM ExpenseMaster A
LEFT JOIN LedgerAddress AS B ON A.LedgerID = B.LedgerID
GROUP BY A.LedgerID, B.LedgerCity;
END

Answer 2

If you are sure, that no one from outside of the database can run your query and perform sql-injection, just use the simple dynamic-sql statement
DECLARE #sql AS NVARCHAR(MAX);
DECLARE #chk AS INT= 0;
set #sql = N'SELECT a.Ledgerid,
b.LedgerCity, ' +
CASE WHEN #chk = 0 THEN 'SUM(a.TotalAmount) ' ELSE 'SUM(a.NetAmount) ' END +
CASE WHEN #chk = 0 THEN ', c.ledgername ' ELSE ' ' END +
'FROM ExpenseMaster A
LEFT JOIN LedgerAddress AS B ON A.LedgerID = B.LedgerID ' +
CASE WHEN #chk=0 THEN 'LEFT JOIN LedgerMaster AS C ON A.LedgerID = C.LedgerID ' ELSE '' END +
'GROUP BY A.LedgerID,
B.LedgerCity' +
CASE WHEN #chk = 0 THEN ', C.LedgerName;' ELSE ';' END;
exec sp_executesql #sql