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  Capstone Project Partitioned table /dbs

  Posted by philsing24 on December 21, 2022 at 12:00 am

  Hi,

  ls /dbs  // I get  the 4 partitioned values
  “2020.08.03”
  “2020.08.04”
  “2020.08.05”
  “2020.08.06”
  “sym”

  I don’t understand what sym represents.
  when I type cols trade, I don’t see the column sym but I can still run the following statement
  select sym from trade where date=2020.08.05

  what’s the difference between option_id and sym? I see only two 2 differences. Sym contains two more rows containing B and  S ?!

  sym
  —————–
  B
  FB20200720C230
  FB20200720C240

  ….

  S

   

  philsing24 replied 6 months, 3 weeks ago 2 Members · 1 Reply
• 1 Reply

• 

  rocuinneagain

  Member

  December 21, 2022 at 12:00 am

  The sym file contains enumerated symbols for an symbol column in any table.

   

  The reason you can select it is that if q fails to find a column of that name it will try to use a global variable , which sym will be.

   

  q)`:tab/ set .Q.en[`:.] ([] a:1 2 3;b:`a`b`c) 
  `:tab/ 
  
  q)tab:get 
  `:tab/ 
  
  q)tab 
  a b 
  --- 
  1 a 
  2 b 
  3 c 
  
  q)select sym from tab 
  sym 
  --- 
  a 
  b 
  c 
  
  q)sym //sym is in memory 
  `a`b`c 2
  
  q)nonsense:`one`two`three 
  
  q)select nonsense from tab //nonsense is not a column but a global variable 
  nonsense 
  -------- 
  one 
  two 
  three 
  
  q)delete sym from `. /delete sym from memory 
  `. 
  
  q)tab / now any sym columns show indexes as they cannot resolve their text 
  a b 
  --- 
  1 0 
  2 1 
  3 2

   

  Review some documentation on enumeration and on disk data:

  • https://code.kx.com/q/basics/enumerations/
  • https://code.kx.com/q4m3/14_Introduction_to_Kdb+/#1428-working-with-sym-files

   

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