Is this possible? range query

Question

I have a db with keys/data as the following
Key data
AA data1
AB data2
AA data3
AB data4
AA data5
AB data6
what I expect is
if search by key =AA return data1,3,5,
if searcy by key = A, return all records
when I query using DB_SET_RANGE
query A, only get all records with key ==AA
seems this is correct output based on the API description, while this is not so-called range query.
is it possible to get what I expect above? use a new BTree comparsion function? if so, AA and AB is treated as the same key, and will not be able to differentiate AA and AB.
right?
there are several threads on this, did not the answer. thanks
The DB_SET_RANGE flag is identical to the DB_SET flag, except that in the case of the Btree access method, the key is returned as well as the data item and the returned key/data pair is the smallest key greater than or equal to the specified key (as determined by the Btree comparison function), permitting partial key matches and range searches

Answer 1

Hi,
Let's consider your database:
key data
AA data1
data3
data5
AB data2
data4
data6
If you do a DBC->c_get() with DB_SET_RANGE and as search key "A" than the cursor will be positioned on the first key/data pair AA - data1. This is correct and complies with the documentation. If you than iterate with DB_NEXT on the DBC->c_get() call (as presented in the previous range_query function) you will sequentially retrieve each record within the database (the records are sorted lexically by key, and duplicates are sorted lexically on the data portion - by default). When you iterate with DB_NEXT_DUP on the DBC->c_get() call you will retrieve the records with the "AA" key.
If you do the DBC->c_get() with DB_SET_RANGE and a search key "AA" than the cursor will be positioned, as in the previous case, on the first key/data pair AA - data1. The same applies when iterating with DB_NEXT or DB_NEXT_DUP.
When you do a range search on "AA" and iterate with DB_NEXT you will get all the records because all the records have the key equal or greater (lexically) than "AA".
The same goes for a range search on "A" and iterating with DB_NEXT.
If you expect to get data1, data 2, data3 when searching on "AA" than this is not a range search, it is a simple query (done with DB_SET initially and than iterate with DB_NEXT_DUP).
If you use the function that I posted previously (exactly as it is) and you pass it "A" as searchKey then you will retrieve all the records, just as you expected.
Here is an excerpt from the documentation:
DB_SET
    Move the cursor to the specified key/data pair of the database, and return the datum associated with the given key.
    The DBcursor->c_get method will return DB_NOTFOUND if DB_SET is set and no matching keys are found. The DBcursor->c_get method will return DB_KEYEMPTY if DB_SET is set and the database is a Queue or Recno database, and the specified key exists, but was never explicitly created by the application or was later deleted. In the presence of duplicate key values, DBcursor->c_get will return the first data item for the given key.
DB_SET_RANGE
    The DB_SET_RANGE flag is identical to the DB_SET flag, except that in the case of the Btree access method, the key is returned as well as the data item and the returned key/data pair is the smallest key greater than or equal to the specified key (as determined by the Btree comparison function), permitting partial key matches and range searches.I hope this clarifies the way to deal with a range query, if not then let me know and I will present a program that demystifies this.
Best regards,
Andrei