如何在上个月的记录中添加1并将其作为当前月份的记录插入？

Question

My table structure is like below

id     month      year  dummyval
11     January    2017  1
12     January    2017  1
13     January    2017  2

I am inserting next month to this table but I also want to insert a dummyval for each id. Like the table should be-

id     month       year  dummyval
11     January     2017  1
12     January     2017  1
13     January     2017  2
11     February    2017  2
12     February    2017  2
13     February    2017  3

How to do that? Please help.

Answer 1

Try this:

insert into table1 select id , 'February', 2017, dummyval+1 from table1  
where id=11;

with each insert you do..

Here's an example:

mysql> select * from K3;
+------+------+
| name | val  |
+------+------+
| x    | 1    |
| y    | 2    |
+------+------+

INSERTING:

insert into K3 select 'g', val+1 from K3 where name='x';

AFTER INSERT:

mysql> select * from K3;
+------+------+
| name | val  |
+------+------+
| x    | 1    |
| y    | 2    |
| g    | 2    |
+------+------+

You can see that it has inserted 'g' with 2, incremented from x's 1

Answer 2

Since you store the month name in your code, you need to have a way to find the next month name. To keep it simple (but somewhat lengthy), I would begin by defining an auxiliary data structure to hold basic month information:

create table months (monthid int, monthname varchar(20));
insert into months (monthid, monthname)
select 1, 'January' union all
select 2, 'February' union all
select 3, 'March' union all
/*... all other months*/
select 12, 'December';

Suppose now that your max year-month value in your table (call it 'data') is 2017/January. You could use the following code to find the next year-month-dummyval combination and insert it into your table, without having to know beforehand which records you need to insert (and their ids):

/* a temporary table to hold "next month" info. It should be avoided using a 
join, but I failed miserably in my attempt! */
create temporary table next_month (monthid int, monthname varchar(20), next_id int, next_name varchar(20));

insert into next_month (monthid, monthname, next_id)
select monthid, monthname, case when monthid = 12 then 1 else monthid + 1 end
from months;

update next_month set next_name = 
 (select monthname from months where months.monthid = next_month.next_id);

Now you are ready to insert your new data:

insert into data (month, year, dummyval)
select 
  next_month.next_name, 
  case when months.monthid = 12 then data.year + 1 else data.year end,
  data.dummyval + 1
from data join months on data.month = months.monthname 
join next_month on months.monthid = next_month.monthid
where data.month = 'January' and data.year = 2017;