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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,
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2 Replies
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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
62.
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))-
got it, thanks!
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