Why can't I select or update the Record using the PreparedStatement?

Question

the DB is oracle9i,here is the test table
test
id number;
name char(10);
intro char(10);
I have insert a record in the table.
Now I will select or update the record by using the PreparedStatement here is my code:
sqlStr = "update test set intro = ? where name =?";
PreparedStatement stmt = conn.prepareStatement(sqlStr);
stmt.setString(1,"my name is irixwang");
stmt.setString(2,"irixwang");
int is = stmt.executeUpdate();
if (is >=1 )
System.out.println("ok");
It will not work ,but where I change the update condiction as followed:
sqlStr = "update test set intro = ? where id =?";
PreparedStatement stmt = conn.prepareStatement(sqlStr);
stmt.setString(1,"my name is irixwang");
stmt.setInt(2,100);
int is = stmt.executeUpdate();
It works well,why?
please help me!thk!!!!

Answer 1

I doubt it works "well" in either case since you are inserting a string that is longer than 10 characters into a field that only holds 10 characters. But to your question....
A char data type holds a fixed number of characters - in your case 10.
Because it holds 10 characters it will never hold 9, regardless of what you think is in the field it will always have 10 characters in it. The value you are using for query for name is 9 characters. Since 9 characters, regardless of content, will never be equal to 10 characters there is no way that it will update.
So your choice is to either use a varchar, which holds a variable number of characters, or to always use 10 characters for your query (pad it with spaces.)