Question

I have a table include some data like that. This is example for question/answer script. ID is auto increment and if PID=0 then it is question, when reply any question then PID is set to question’s ID. There is no Subject for replies.

ID    PID    SUBJECT                CONTENT                   DATE
1      0     First Question         This is my first          09/01/2013
2      0     Second Question        This is second            09/01/2013
3      1                            Yes this is first         09/01/2013
4      2                            I agree this is second    10/01/2013
5      0     Third Question         This is third question    11/01/2013
6      1                            Reply to first            11/01/2013
7      1                            Another reply to first    12/01/2013
8      5                            This is reply of 5th      13/01/2013
9      2                            Last try for second       14/01/2013

My questions are,

How can I select questions with reply count?

Ex.
First Question (3)
Second Question (2)
Third Question (1)

How can I select today’s answered questions or answers?

Ex. For 09/01/2013
First Question (2) ---> 1 question and 1 answer but 2 actions
Second Question (1) ---> just 1 question

Answer 1

Try join for first task

SELECT 
    q.id as ID,
    q.pid as PID,
    q.subject as SUBJECT,
    COUNT(lq.id) as Total
FROM questions as q
LEFT JOIN questions as lq ON lq.pid = q.ID
WHERE q.PID = 0
GROUP BY q.id

OUTPUT

ID  PID     SUBJECT             TOTAL
1   0       First Question      3
2   0       Second Question     2
5   0       Third Question      1

Demo

EDITS :
For second part. You should note that there can be many other ways for doing the same task.

SELECT 
    q.id as ID,
    q.pid as PID,
    q.subject as SUBJECT,
    (COUNT(lq.id) - 1) as Total,
    q.date
FROM questions as q
LEFT JOIN questions as lq ON lq.pid = q.ID OR lq.id = q.PID
WHERE q.date = DATE(NOW())

OUTPUT

ID  PID     SUBJECT             TOTAL   DATE
1   0       First Question      2       January, 09 2012 00:00:00+0000
2   0       Second Question     1       January, 09 2012 00:00:00+0000

Demo