Try this, you are missing “+”s and “‘”s:
DECLARE @SQL NVARCHAR(MAX) = N'
SELECT
CASE WHEN ISNULL(10, '''') = '''' AND ISNULL('''', '''') = '''' THEN ''''
ELSE CONVERT(NVARCHAR(5), 10) + ' + ''' To ''' + ' + CONVERT(NVARCHAR(5), 20)
END;';
SELECT @SQL;
EXEC(@SQL);
1
solved syntax error while executing sql [closed]