KDB: user-defined aggregation function on tables

Question

Consider a simple user-defined aggregation function MySum:{sum x}, and consider the table

data:([]y:1 8 27 64 125;x1:1 2 3 4 5;x2:1 4 9 16 25).  

Why does the following not work?

select MySum{x}x2 from data
`rank

Answer 1

You can use :

 q)select enlist MySum x2 from data

Why 'select Mysum x2 from data' doesn't work?

From KDB WIKI: "The following functions receive special treatment within select

count,first,last,sum,prd,min,max,med,avg,wsum,wavg,var,dev,cov,cor "

For Details, read: http://code.kx.com/q/ref/qsql/#select

Section: Special functions within select