MYSQL - Selecting data from second row in a large table

问题

I have an external 3rd party program export the database to mysql in real time, and I want to show data for reporting. So, I can't change the structure, because it's being sync in real time.

The table structure is something like this

ID | Date       | Transaction
-----------------------------
12 | 2012-11-01 | 200
12 | 2012-11-02 | 250
12 | 2012-11-03 | 150
12 | 2012-11-04 | 1000
12 | 2012-11-05 | 225
....
13 | 2012-11-01 | 175
13 | 2012-11-02 | 20
13 | 2012-11-03 | 50
13 | 2012-11-04 | 100
13 | 2012-11-05 | 180
13 | 2012-11-06 | 195

The data are very large and keep getting bigger each day.

What I want to do is to build a report (view table) based on something like this:

ID | Date       | Transaction | Prev Day Transaction
----------------------------------------------------
12 | 2012-11-01 | 200         | 0
12 | 2012-11-02 | 250         | 200
12 | 2012-11-03 | 150         | 250
12 | 2012-11-04 | 1000        | 150
12 | 2012-11-05 | 225         | 1000
....
13 | 2012-11-01 | 175         | 0
13 | 2012-11-02 | 20          | 175
13 | 2012-11-03 | 50          | 20
13 | 2012-11-04 | 100         | 50
13 | 2012-11-05 | 180         | 100
13 | 2012-11-06 | 195         | 180

I just can't get the fast select statement. Currently the original data is already 283,120 rows. And it will grow like 500 rows daily.

I've tried something like:

SELECT *, (SELECT transaction FROM table as t2 WHERE t1.id=t2.id 
AND t1.date>t2.date ORDER BY t2.date DESC LIMIT 0,1)
FROM table AS t1

It's working, but the select statement is very slow. Most of the time, it's getting cut of in the middle of the operation.

What I need help is a very fast sql statement, which later on I could use to build the view table.

回答1:

See this link: http://sqlfiddle.com/#!2/54a5e/12

select t.id,t.cDate,t.cTrans
  ,(case when @pID=t.id then @pTran else 0 end) as preT 
  ,(@pID :=t.id) as `tID`,(@pTran := t.cTrans) as `tTrans` 
from tb_test_1 as t,(select @pID = 0, @pTran = 0) as t2
order by id,cDate;

tID and tTrans column must be retained, and cannot display on page.

Please forgive me as I only know a little english!

回答2:

Try this query -

SELECT t1.*, COALESCE(t2.transaction, 0) Prev_Day_Transaction FROM trans t1
  LEFT JOIN (SELECT * FROM trans ORDER BY id, date DESC) t2
    ON t1.id = t2.id AND t1.date > t2.date
GROUP BY t1.id, t1.date;

+------+------------+-------------+----------------------+
| id   | date       | transaction | Prev_Day_Transaction |
+------+------------+-------------+----------------------+
|   12 | 2012-11-01 |         200 |                    0 |
|   12 | 2012-11-02 |         250 |                  200 |
|   12 | 2012-11-03 |         150 |                  250 |
|   12 | 2012-11-04 |        1000 |                  150 |
|   12 | 2012-11-05 |         225 |                 1000 |
|   13 | 2012-11-01 |         175 |                    0 |
|   13 | 2012-11-02 |          20 |                  175 |
|   13 | 2012-11-03 |          50 |                   20 |
|   13 | 2012-11-04 |         100 |                   50 |
|   13 | 2012-11-05 |         180 |                  100 |
|   13 | 2012-11-06 |         195 |                  180 |
+------+------------+-------------+----------------------+

Add composite index (id, date) to the table.

===========================

ALTER TABLE mt4_daily
  ADD INDEX IX_mt4_daily_DATE (DATE);

ALTER TABLE mt4_daily
  ADD INDEX IX_mt4_daily (ID, DATE);

回答3:

Divide the table into few pars through select statements and join them using UNION Set operator. As all set operators are parallel operation you will get the data very quickly. You can divide the data by using the Unique numeric column in your table. e.g.

select * from tbl_x where col1%3=0 union
select * from tbl_x where col1%3=1 union
select * from tbl_x where col1%3=2 ...

The above sql query divides the data and fetches in parallel way

回答4:

I would try to write the query like this:

SELECT
  tbl.ID,
  tbl.Date,
  tbl.Transaction,
  COALESCE(tbl1.Transaction,0) as PrevDay
FROM
  tbl left join tbl tbl1
  on tbl.ID = tbl1.ID
     and tbl.Date = tbl1.Date + INTERVAL 1 DAY

(this will work only if you make sure that the table contains all days, if you miss one day, the next day will always show PrevDay as 0, i am not sure if this is what you need).

EDIT: i would try this solution that works even if some days are missing:

SELECT
  tbl.id,
  tbl.date,
  tbl.Transaction,
  COALESCE(tbl1.Transaction,0) as PrevDay
FROM
  (SELECT tbl.id, tbl.date as d1, max(tbl1.ddate) as d2
   FROM tbl LEFT JOIN tbl tbl1
        ON tbl.id = tbl1.id and tbl.date>tbl1.date
   GROUP BY tbl.id, tbl.date) t
  LEFT JOIN tbl on tbl.id = t.id and DATE(tbl.ddate) = DATE(t.d1)
  LEFT JOIN tbl tbl1 ON tbl1.id = t.id and DATE(tbl1.date) = DATE(t.d2)

来源：https://stackoverflow.com/questions/13560266/mysql-selecting-data-from-second-row-in-a-large-table

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mysql

optimization

select

row