qSQL questions _ where clause and exec results

Academy Support
1

https://learninghub.kx.com/forums/topic/qsql-questions-_-where-clause-and-exec-results

Trying to combine two questions in one post as both are qSQL related, apologies if any confusions.


1. Q statement follows right to left, is it also the case when processing multi where conditions? e.g.


select from smalltrade2 where size=first size,sym=`GE

It seems from the notebook Q first read size and then sym in the where clause, so where does not right to left order?


2. below example from the notebook--why only assignment to a symbol would return a keyed table, when the sym itself is already in the table daily?


exec first open, last close by sym from daily where sym like "*L" //not a keyed table, a dictionary

exec first open, last close by sym:sym from daily where sym like "*L" //keyed table - also a dictionary


Thanks,

2

1. qSQL has some differences to q.

https://code.kx.com/q/ref/select/

"select is a qSQL query template and varies from regular q syntax."

https://code.kx.com/q/basics/qsql/#where-phrase

"Efficient Where phrases start with their most stringent tests."

Each where clause is it's own expression. You can see inside [] the expression are executed left to right but within each expression the code is executed right to left. 

q)[(show 2;show 1);(show 4;show 3);(show 6;show 5)];
1
2
3
4
5
6

2.

https://code.kx.com/q/basics/funsql/#group-by-column

"b is a column name. The result is a dictionary."

https://code.kx.com/q/basics/funsql/#group-by-columns

"b is a list of column names. ... returns a dictionary"

https://code.kx.com/q/basics/funsql/#group-by-a-dictionary

"b is a dictionary. Result is a dictionary in which the key is a table with columns as specified by b ..."

If you parse the queries you can see that sym:sym is group by dictionary


q)parse"exec first open, last close by sym from daily where sym like \"*L\""
?
`daily
,,(like;`sym;"*L")
,`sym
`open`close!((*:;`open);(last;`close))


vs:


q)parse"exec first open, last close by sym:sym from daily where sym like \"*L\""
?
`daily
,,(like;`sym;"*L")
(,`sym)!,`sym
`open`close!((*:;`open);(last;`close))
3

got it, thanks!