Inner join

x ij y ij [x;y] x ijf y ijf[x;y]

Where

returns two tables joined on the key columns of the second table. The result has one combined record for each row in x that matches a row in y.

q)t
sym  price
---------------
IBM  0.7029677
FDP  0.08378167
FDP  0.06046216
FDP  0.658985
IBM  0.2608152
MSFT 0.5433888

q)s
sym | ex  MC
----| --------
IBM | N   1000
MSFT| CME 250

q)t ij s
sym  price     ex  MC
-----------------------
IBM  0.7029677 N   1000
IBM  0.2608152 N   1000
MSFT 0.5433888 CME 250

Common columns are replaced from y.

q)([] k:1 2 3 4; v:10 20 30 40) ij ([k:2 3 4 5]; v:200 300 400 500;s:`a`b`c`d)
k v   s
-------
2 200 a
3 300 b
4 400 c