null (null function)
The function null returns 1b if its argument is null.
Applies to all data types except enums. Applies item-wise to lists, dict values and table columns.
q)null 0 0n 0w 1 0n 01001b
Enums always show as non-null.
q)a:``a q)`=`a$` / non-enumerated and enumerated null symbol show as equivalent 1b q)null` / null symbol behaves as expected 1b q)null`a$` / enumeration of null symbol does not 0b
The intention was not to have nulls in the enums. That value is used to indicate "out of range". (Think of them as a way to represent foreign keys.) To test for an enumeration backed by a null symbol, one can use the equality test - but at the cost of CPU cycles:
q)a:10000000?`8 q)v:`a$a q)\ts null v 18 16777344 q)\ts `=v 66 268435648 q)
For a complete list of functions, see the kdb+ Function Reference.