[amcnaught921]

Hey,

 

The following will give the solution you require

q)t1
TimeStamp stock p1 p2
----------------------
2018.01.01 AAPL 1 -1
2018.01.01 AAPL 2 1
2018.01.02 GOOGL -2 2
2018.01.02 GOOGL 3 0

q)f:{$[0=x+y;0;x*y]}

q)t1:update r:f'[p1;p2] from t1

TimeStamp stock p1 p2 r
------------------------
2018.01.01 AAPL 1 -1 0
2018.01.01 AAPL 2 1 2
2018.01.02 GOOGL -2 2 0
2018.01.02 GOOGL 3 0 0

Some documentation on $ also here: https://code.kx.com/q/ref/cond/

[amcnaught921]

Hello,

 

It is somewhat hard to fully answer without seeing the data, but I mocked up the following
test:([] TRADE_DT:enlist .z.d; S_INFO_WINDCODE:`test; S_DQ_CLOSE:1.1; S_DQ_AMOUNT:2.2; S_DQ_VOLUME: 3.3)

meta test
c | t f a
—————| —–
TRADE_DT | d
S_INFO_WINDCODE| s
S_DQ_CLOSE | f
S_DQ_AMOUNT | f
S_DQ_VOLUME | f

And from this I could do your simple select statement, there are scenario’s where column name can cause issues with select statements (e.g. if they started with underscores), in this case you can use functional select (however not required here I will post for this simple example)
?[`test;();0b;(enlist `TRADE_DT)!enlist `TRADE_DT]

Both returned:

TRADE_DT
———-
2024.01.17