mysql: duplicate certain rows using SQL? - sql

Question

I have a table that looks like this:
nid vid tid
1 2 3
2 2 4
3 2 4
4 2 3
I'd like to run some SQL that will take each one of those rows and create another based on it like so:
foreach row where vid=2, create a duplicate row where vid = 3
So I'll end up with this:
nid vid tid
1 2 3
2 2 4
3 2 4
4 2 3
1 3 3
2 3 4
3 3 4
4 3 3
The table is not that big (less than 500 rows, I think) and this is a one-time thing (so the code does not need to be amazingly optimized or anything). Thanks!

Answer 1

you’ll probably want this:
INSERT INTO `table`(`nid`, `vid`, `nid`)
SELECT `nid`, `vid`+1, `nid`
FROM `table`
WHERE `vid` = 2
it inserts all rows, with vid incremented by 1

Answer 2

If you want a general solution (i.e. all values of vid, but adding one to each of them), this is just adapting dandres' answer:
INSERT INTO TheTable(nid, vid_incremented, nid)
SELECT nid, vid + 1 as vid_incremented , nid
FROM TheTable
Edit: fixed to do arithmetic in select statement.

Answer 3

Could you do the following:
INSERT INTO TheTable(nid, vid, nid)
SELECT nid, 3, nid
FROM TheTable
WHERE vid = 2
Two columns appear to have the same name, but the above should work. It takes the set of Vid = 2 elements, inserts them again but using Vid = 3.

Answer 4

Create another table with 2 fixed records, e.g. TwoRec (vvid), with values 2 and 3
Do a cartesian join with TwoRec, i.e.
SELECT TheTable.nid, TwoRec.vvid, TheTable.nid
FROM TheTable, TwoRec
WHERE TheTable.vid = 2;

Answer 5

I'd create a temp table of all of the vids you want to use:
create temporary table Vids
(
vid int
)
declare #vid int
declare #maxvid int
set #vid = 1
set #maxvid = 500
while #vid < #maxvid
begin
insert into vids values(#vid)
set #vid = #vid + 1
end
Then, I'd use that temp table to build out your other table:
select
t2.id,
t1.vid,
t2.nid
into newtable
from
vids t1
cross join tbl t2
order by
t1.vid,
t2.id