To check if a table exists and append a file

Community Support
1

Hi,

Two questions

1.. I want to know if the table exists,if not I want to create a table.(table=typed table)

  1. In order to save a table ,save command would create a file on the disk.But it creates a new file and removes the old content.How can I append to the existing file

Thanks.

2

Hi,

The upsert function will solve both of those in one go. It will create a table if it doesn’t exist and append to the if it already exists.

q)key `:/db  //returns nothing indicating trade doesn’t exist in db

q)

q)

q):/db/trade upsert ([]time:4?.z.t;sym:4?JPM`GE;price:4?10f)

`:/db/trade  //table has been created

q)

q)get `:/db/trade

time         sym price

12:25:01.416 JPM 4.101914

08:34:04.468 JPM 2.337549

01:02:27.466 JPM 7.125845

02:24:40.646 GE  1.392257

q)

q)

q):/db/trade upsert flip(5?.z.t;5?BP`AAPL;5?20f)  //this will append to the table without overwriting

`:/db/trade

q)

q)

q)get `:/db/trade

time         sym  price

12:25:01.416 JPM  4.101914

08:34:04.468 JPM  2.337549

01:02:27.466 JPM  7.125845

02:24:40.646 GE   1.392257

12:12:45.199 BP   19.59219

09:44:09.076 AAPL 6.154981

01:51:55.498 BP   7.304546

13:05:09.588 AAPL 19.18235

07:23:39.994 BP   8.243732

Note: If the table you are appending to is a keyed table, then upsert will overwrite the key if it already exixts. In the case you don’t want that, you can use the insert function which will throw an error if that key already exists.

Regards,

Jason

Jason Fealy | Kx Engineer | Kx | +1 (718) 340-9791 | jfealy@kx.com