合并表/联接查询MySql

Question

I am stuck with this query and I am not able to solve it. I need help in joining tables.

I have 4 tables (customer, product, status and offer).

I want to read from these tables based on customer ID.

In first 3 tables, the number of record against customer ID is one, but offer table may have more than one rows for a customer.

I want to read the latest row from the offer table for each customer. I am not able make a query for this situation.

For example

Customer have columns (cID, Name, Surname)
STATUS (sID, cID, Status, Sdate)
ADDRESS (adID, cID, Addetail)
Offer (ID, cID, offer, offDate)

Here is my query, which is not working:

SELECT c.ID, 
c.NAME, 
c.SURNAME, 
st.ID, 
st.Status, 
st.Sdate
ad.Addetial,
off.OffDATE
FROM customer c, address ad, status st, offer of

WHERE 
c.ID=ad.cID 
AND c.ID=st.cID 
AND c.ID = off.cID
.. 

I am confuse how to restrict the selection to one row from the offer table. because if I put c.ID = off.cID then it will return all the offers which I don't want.

PS: I know there are similar questions, but I couldn't map it according to my situation. Using Max, returns only one row (even if there are many customers).

Answer 1

Try this one

SELECT c.ID, 
c.NAME, 
c.SURNAME, 
st.ID, 
st.Status, 
st.Sdate
ad.Addetial,
off.OffDATE
FROM customer c   
WHERE 
INNER JOIN  address ad ON c.ID=ad.cID 
INNER JOIN  status st  ON AND c.ID=st.cID 
INNER JOIN (SELECT *,MAX(id) AS `max` FROM offer GROUP BY  id ,cID) off
ON c.ID = off.cID

I have used a subquery (SELECT *,MAX(id) AS max FROM offer GROUP BY id ,cID) to get the latest customer offers subquery will execute only once to get the desired latest dataset

Answer 2

You want the groupwise maximum , which can be obtained by joining the offer table to a grouped version of itself:

SELECT c.ID,
       c.NAME, 
       c.SURNAME, 
       st.ID, 
       st.Status, 
       st.Sdate
       ad.Addetial,
       off.OffDATE
FROM   customer c
  JOIN address  ad ON ad.cID = c.ID
  JOIN status   st ON st.cID = c.ID
  JOIN (offer  off NATURAL JOIN (
         SELECT   cID, MAX(OffDATE) OffDATE
         FROM     offer
         GROUP BY cID
       ) t) ON off.cID = c.ID