adding a new row when particular combination is not available, otherwise update a field

I have table with following structure

id         int             auto increment, primary key
uid        int             (comment: userid)
cdt        date/time       (comment: current date)
hits 开发者_运维百科      int             (comment: no. of hits)

Now, I need a query such as

for a particular combination of 'uid' and 'cdt', if there is row available, then update hits (ie., add 1 to hits) otherwise add new row with 'uid' and 'cdt' values, and hits set to 1

Let me clear further with example

say uid = 01, and cdt = 2010-01-01, if this combination of uid and cdt is not available in table, then new row should be inserted, otherwise value of hits should be update

How to achieve this?

You could do this in two steps:

First:
Query db to know if that particular record is present:

SELECT id FROM your_table 
WHERE uid = your_user_id AND cdt = your_date 

Second:
If previous query returns zero rows:

INSERT INTO your_table
(uid, cdt, hits)
SELECT your_user_id, your_date, 1

else:

UPDATE your_table
SET hits = hits + 1
WHERE uid = your_user_id AND cdt = your_date