Question: I have a table of strings in my database. I select one of them, *A*.

How I can search the rest of the table to find the string most similar to *A*?

Answer: 
I think you are looking for the levenstein distance.
The levenstein distance between 2 string, is how much adding/deleting/modifying char is needed to make the string equals.

[Here's an implementation in Ruby](https://github.com/threedaymonk/text)
If you are after the phonetic similarity between two strings, you could use the SQL soundex function (there is also metaphone in Oracle). 

This will convert the string passed to it into a 4 digit code (1 letter, 3 numbers iirc) which represents the phonetic sound of the word(s).

If you do this to both of the strings you are comparing, if they are phonetically similar then you can match the codes.