mysql左连接只从基本表的第一行

Question

I am hard thinking about how to LEFT JOIN data from one table to the BASE table .. but only for the FIRST row from base table ... is that even possible?

For example:

TABLE1

item_id  |  insert_datetime  |  value  
---------------------------------------
   2     | 1/1/2014 12:54:05 |   65
   2     | 1/1/2014 12:57:05 |   65
   3     | 8/7/2014 10:01:47 |   87
   3     | 9/8/2014 09:37:21 |   33
   3     | 9/8/2014 09:42:21 |   33
   4     | 2/9/2014 15:22:01 |   58

TABLE2 (left-joined by ID, date [not datetime], value)

item_id  |   drop_datetime   |  value  
---------------------------------------
   2     | 1/1/2014 00:00:00 |   65
   3     | 9/8/2014 00:00:00 |   33

I need to do something like this:

SELECT t1.item_id
, t1.insert_datetime as inserted
, t1.value as ins_value
##
, t2.drop_datetime as cancelled
, t2.value as cld_value
##
FROM table1 t1
##
LEFT JOIN table2 t2
ON t2.item_id = t1.item_id
AND date(t2.drop_datetime) = date(t1.insert_datetime)
AND t1.value = t2.value
##
WHERE 1=1

So it means I need to get which values were cancelled ... but in case of item_id = 2 there was following situation:

Item was shipped on 1/1/2014 12:54:05 (with value 65) ... it was cancelled (1st row in T2), because of wrong parameters and was reshipped 1/1/2014 12:57:05 with the same value

What I get for item_id = 2 is:

item_id  |     inserted      |  ins_value |  cancelled        |   cld_value
-----------------------------------------------------------------------------
   2     | 1/1/2014 12:54:05 |     65     | 1/1/2014 00:00:00 |      65
   2     | 1/1/2014 12:57:05 |     65     | 1/1/2014 00:00:00 |      65

But I NEED to get this:

item_id  |     inserted      |  ins_value |  cancelled        |   cld_value
-----------------------------------------------------------------------------
   2     | 1/1/2014 12:54:05 |     65     | 1/1/2014 00:00:00 |      65
   2     | 1/1/2014 12:57:05 |     65     |                   |       

Because in reality, was only the first cancelled.. is is possible to get this result in MySQL?

NOTE: And an item also could be, unfortunatelly, cancelled for two or threetime in an hour

                                   **EDIT 1**

If it helps ... all data are in one table with symptom of SHIP(1) or CANCLED(2)

SOURCE TABLE

id  |  item_id  |  insert_datetime  |  value  |  symptom  
-----------------------------------------------------------
1   |     2     | 1/1/2014 12:54:05 |   65    |     1
2   |     2     | 1/1/2014 00:00:00 |   65    |     2
3   |     2     | 1/1/2014 12:57:05 |   65    |     1
4   |     3     | 8/7/2014 10:01:47 |   87    |     1
5   |     3     | 9/8/2014 09:37:21 |   33    |     1
6   |     3     | 9/8/2014 00:00:00 |   33    |     2
7   |     3     | 9/8/2014 09:42:21 |   33    |     1
8   |     4     | 2/9/2014 15:22:01 |   58    |     1

will this help?

                                   **POSSIBLE SOLUTION**

Ít seems that this works ok:

SELECT t1.item_id
, t1.insert_datetime as inserted
, t1.value as ins_value
##
, t2.drop_datetime as cancelled
, t2.value as cld_value
##
FROM table1 t1
##
LEFT JOIN table2 t2
ON t2.item_id = t1.item_id
AND date(t2.drop_datetime) = date(t1.insert_datetime)
AND t1.value = t2.value
AND t1.id < t2.id   ## <- this should do the trick
##
WHERE 1=1

Answer 1

You can try this :

SQL Fiddle

MySQL 5.5.32 Schema Setup :

CREATE TABLE Table1
    (`id` int, `item_id` int, `insert_datetime` datetime, `value` int, `symptom` int)
;

INSERT INTO Table1
    (`id`, `item_id`, `insert_datetime`, `value`, `symptom`)
VALUES
    (1, 2, '2014-01-01 12:54:05', 65, 1),
    (2, 2, '2014-01-01 00:00:00', 65, 2),
    (3, 2, '2014-01-01 12:57:05', 65, 1),
    (4, 3, '2014-07-08 10:01:47', 87, 1),
    (5, 3, '2014-08-09 09:37:21', 33, 1),
    (6, 3, '2014-08-09 00:00:00', 33, 2),
    (7, 3, '2014-08-09 09:42:21', 33, 1),
    (8, 3, '2014-08-09 00:00:00', 33, 2),
    (9, 3, '2014-08-09 09:48:29', 33, 1),
    (10, 3, '2014-09-02 15:22:01', 58, 1)
;

Query 1 :

SELECT DISTINCT t1.item_id
, t1.insert_datetime as inserted
, t1.value as ins_value
, ifnull(t2.insert_datetime,'') as cancelled
, ifnull(t2.value,'') as cld_value
FROM table1 t1
LEFT JOIN table1 t2
ON t2.item_id = t1.item_id
AND date(t2.insert_datetime) = date(t1.insert_datetime)
AND t1.value = t2.value
AND t1.id < t2.id 
AND t2.symptom = 2
WHERE t1.symptom = 1 

Results :

| ITEM_ID |            INSERTED | INS_VALUE |           CANCELLED | CLD_VALUE |
|---------|---------------------|-----------|---------------------|-----------|
|       2 | 2014-01-01 12:54:05 |        65 | 2014-01-01 00:00:00 |        65 |
|       2 | 2014-01-01 12:57:05 |        65 |                     |           |
|       3 | 2014-07-08 10:01:47 |        87 |                     |           |
|       3 | 2014-08-09 09:37:21 |        33 | 2014-08-09 00:00:00 |        33 |
|       3 | 2014-08-09 09:42:21 |        33 | 2014-08-09 00:00:00 |        33 |
|       3 | 2014-08-09 09:48:29 |        33 |                     |           |
|       3 | 2014-09-02 15:22:01 |        58 |                     |           |

Answer 2

you can try this

SET @rowNoIn:=0;
SET @RowNoCn:=0;
SET @itemIn='';
SET @itemCn='';

select i.*,c.*
from(
  SELECT 
    @rowNoIn:=CASE WHEN @itemIn=item_id THEN @rowNoIn+1 ELSE 1 END AS rowNo
    ,@itemIn:=item_id AS item_id
    ,insert_datetime
    ,value
  FROM table1
  ORDER BY item_id, insert_datetime
)i
left join (
  SELECT 
    @rowNoCn:=CASE WHEN @itemCn=item_id THEN @rowNoCn+1 ELSE 1 END AS rowNo
    ,@itemCn:=item_id AS item_id
    ,drop_datetime
    ,value
  FROM table2
  ORDER BY item_id, drop_datetime)c
on 
  i.item_id = c.item_id
  and i.rowNo = c.rowNo

sqlFiddle

Note if there is an item cancellation it assumes the first item form table1 is to be cancelled (no matter what date) you can update the code to better suit your need, but hopefully it will lead you into a right direction. You should really consider adding ID to your table1 so you could reference the cancelled records explicitly.