MySQL JOIN the most recent row only?

Question

I have a table customer that stores a customer_id, email and reference. There is an additional table customer_data that stores a historical record of the changes made to the customer, i.e. when there's a change made a new row is inserted.

In order to display the customer information in a table, the two tables need to be joined, however only the most recent row from customer_data should be joined to the customer table.

It gets a little more complicated in that the query is paginated, so has a limit and an offset.

How can I do this with MySQL? I think I'm wanting to put a DISTINCT in there somewhere...

The query at the minute is like this-

SELECT *, CONCAT(title,' ',forename,' ',surname) AS name
FROM customer c
INNER JOIN customer_data d on c.customer_id=d.customer_id
WHERE name LIKE '%Smith%' LIMIT 10, 20

Additionaly, am I right in thinking I can use CONCAT with LIKE in this way?

(I appreciate that INNER JOIN might be the wrong type of JOIN to use. I actually have no clue what the difference is between the different JOINs. I'm going to look into that now!)

Answer 1

SELECT CONCAT(title,' ',forename,' ',surname) AS name * FROM customer c 
INNER JOIN customer_data d on c.id=d.customer_id WHERE name LIKE '%Smith%' 

i think you need to change c.customer_id to c.id

else update table structure

Answer 2

It's a good idea that logging actual data into "customer_data" table. With this data you can select all data from "customer_data" table as you wish.

Answer 3

This might help

http://stackoverflow.com/questions/435703/how-to-select-the-most-recent-set-of-dated-records-from-a-mysql-table

You can use a subquery to get the most recent record(s) then join to your customer.

Answer 4

You may want to try the following:

SELECT    CONCAT(title, ' ', forename, ' ', surname) AS name
FROM      customer c
JOIN      (
              SELECT    MAX(id) max_id, customer_id 
              FROM      customer_data 
              GROUP BY  customer_id
          ) c_max ON (c_max.customer_id = c.customer_id)
JOIN      customer_data cd ON (cd.id = c_max.max_id)
WHERE     CONCAT(title, ' ', forename, ' ', surname) LIKE '%Smith%' 
LIMIT     10, 20;

Note that a JOIN is just a synonym for INNER JOIN.

Test case:

CREATE TABLE customer (customer_id int);
CREATE TABLE customer_data (
   id int, 
   customer_id int, 
   title varchar(10),
   forename varchar(10),
   surname varchar(10)
);

INSERT INTO customer VALUES (1);
INSERT INTO customer VALUES (2);
INSERT INTO customer VALUES (3);

INSERT INTO customer_data VALUES (1, 1, 'Mr', 'Bobby', 'Smith');
INSERT INTO customer_data VALUES (2, 1, 'Mr', 'Bob', 'Smith');
INSERT INTO customer_data VALUES (3, 2, 'Mr', 'Jane', 'Green');
INSERT INTO customer_data VALUES (4, 2, 'Miss', 'Jane', 'Green');
INSERT INTO customer_data VALUES (5, 3, 'Dr', 'Jack', 'Black');

Result (query without the LIMIT and WHERE):

SELECT    CONCAT(title, ' ', forename, ' ', surname) AS name
FROM      customer c
JOIN      (
              SELECT    MAX(id) max_id, customer_id 
              FROM      customer_data 
              GROUP BY  customer_id
          ) c_max ON (c_max.customer_id = c.customer_id)
JOIN      customer_data cd ON (cd.id = c_max.max_id);

+-----------------+
| name            |
+-----------------+
| Mr Bob Smith    |
| Miss Jane Green |
| Dr Jack Black   |
+-----------------+
3 rows in set (0.00 sec)

Answer 5

Presuming the autoincrement column in customer_data is named Id, you can do:

SELECT CONCAT(title,' ',forename,' ',surname) AS name *
FROM customer c
    INNER JOIN customer_data d 
        ON c.customer_id=d.customer_id
WHERE name LIKE '%Smith%' LIMIT 10, 20
    And d.ID = (
                Select Max(D2.Id)
                From customer_data As D2
                Where D2.customer_id = D.customer_id
                )