Re: parse tree not working for simple select - KX Learning Hub

davidcrossey

Member
October 10, 2022 at 12:00 am
As you’ve mentioned parse trees in your post title, I’ll limit the scope of the following examples here using parse on a select statement*;

If you want to carry out of a functional select for both of the queries above, I suggest using the parse keyword to determine the components of the phrase:
```
// c2>16 example 
q)parse "select from tab where c2>16" 
? 
`tab 
,,(>;`c2;16) 
0b
() 

q)?[tab;enlist (>;`c2;16);0b;()] 
c1 c2 
----- 
7 17 
8 18 
9 19 

// last c2 example 
q)parse "select last c2 from tab" 
? 
`tab 
() 
0b 
(,`c2)!
,(last;`c2) 

q)?[tab;();0b;enlist[`c2]!enlist (last;`c2)] 
c2 
-- 
19
```
You can read more about parse here and parse trees here

*There are other ways of retrieving specific values for the queries you’ve listed. For example, you could also write last tab[`c2] to fetch the last value in the c2 column

Hope this helps.