Tweak in Double.ToString() conversion

I am working on an application which involves lot of arithmetic operations. In this application we heavily make use of double and string interchangeably.
I was facing a problem with conversion between double type to string variables.

Consider below code;

1 2	double d = 30.235312769517968; string convertedValue = d.toString();

If we see the output of convertedValue variable it gives us something like 30.235312769518, which fails the comparison.
To preserve the decimal precision we can make use of ToString() as below;

1	string convertedValue = d.ToString("R");

By default, the return value only contains 15 digits of precision although a maximum of 17 digits is maintained internally. If the value of this instance has greater than 15 digits, ToString returns PositiveInfinitySymbol or NegativeInfinitySymbol instead of the expected number. If you require more precision, specify format with the "G17" format specification, which always returns 17 digits of precision, or "R", which returns 15 digits if the number can be represented with that precision or 17 digits if the number can only be represented with maximum precision.

Note that not all the numbers can be represented exactly...

Left outer join using LINQ - yields different outputs

Couple of days ago, I was working on a project where I was supposed to convert SQL queries in LINQ. There was a simple SQL query as;

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SELECT * FROM Table1 td1LEFT OUTER JOIN Table2ON td1.ColumnName = td2.ColumnName WHERE td2.ColumnName IS NULL ORDER BY SomeColumns

I ran this query in SQL Query analyzer, it returned me 100 records. And my converted LINQ code returned me 105 records. I converted this query intto LINQ to perform Left Outer Join as;
I did this in 2 ways;
Method 1:

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var data= (from td1in Table1 join td2 in Table2.Where(a => a.ColumnName == (int?)null) on td1.ColumnName equals td2.ColumnName into outer from x in outer.DefaultIfEmpty() orderby SomeColumns select td1);

Method 2: 

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var data = from td1 in Table1 join td2 in Table2 on td1.ColumnName equals td2.ColumnName into outer from item in outer.DefaultIfEmpty() where item.ColumnName.Value == (int?)null orderby somecolumns select td1 ;

This gave me an exception as, failed to enumerate results 

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var data = from td1 in Table1 join td2 in Table2 on td1.ColumnName equals td2.ColumnName into outer from item in outer.DefaultIfEmpty() where item == null orderby somecolumns select td1 ;

In my original query that line item.ColumnName.Value == (int?)null was wrong, because I tried to retrieve value for all ColumnName even if item was null. I corrected that with the following query and it worked fine.