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Linked Columns and overloads of $ ! ?
I am trying to figure out WHICH overloads of $ ! ? are used in foreign keys and linked columns syntax</div>
Foreign Keys
kt$localColumn
Question 1. Is $ for enum ?
Question 2. kt as a table type is undocumented (but implied) right ?
LinkedColumn
otherTable!otherTable.otherCol?localColumn
Q3. Is ? doing a find
Q4. Is ! doing a dict (as in keyed table is a dict too) way OR “linking” which is undocumented still
Q doc still has some gaps which is why I have come up with these inferences after playing around with the code in the links below for a while. So ideally please gives “yes”/”no” or a big tutorial 😉
Links
https://code.kx.com/q/kb/linking-columns/#splayed-tables
https://code.kx.com/q/wp/foreign-keys/#foreign-keys
code.kx.com
Linking columns | Database | kdb+ and q documentation - kdb+ and q documentation
A link column is similar to a foreign-key column – it provides linkage between the values of a column in a table to the values in a column in a second table
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2 Replies
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The following page has some examples on the different types of enum operations: https://code.kx.com/q/basics/enumerations/
code.kx.com
Enumerations – Basics – kdb+ and q documentation - kdb+ and q documentation
For a long list containing few distinct values, an enumeration can reduce storage requirements.
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Q1. Yes,
$is creating an enum. https://code.kx.com/q/ref/enumerate/ . Could you supply a reproducible case for what the variables represent in the first statement.Q2. KeyedTable (kt?) is documented see https://code.kx.com/q/kb/faq/#keyed-tables.
Q3.
?is doing a find. https://code.kx.com/q/ref/find/>>>t1
c1 c2
—–
c 10
b 20
a 30
>>>c3
`sym$`a`b`a`c
>>>t1.c1?c3
2 1 2 0
Q4. The
!is simply creating an enumeration. If you are then to update the table with the result of that query, it would be added to the table as a foreign key. Documentation exists here. https://code.kx.com/q/ref/enumeration/>>>`t1!t1.c1?c3
`t1!2 1 2 0
>>>update link:`t1!t1.c1?c3 from `t2
`t2
>>>meta t2
c | t f a
—-| ——
c3 | s
c4 | f
link| j t1
The following page has some examples on the different types of enum operations: https://code.kx.com/q/basics/enumerations/
code.kx.com
Enumerate | Reference | kdb+ and q documentation - kdb+ and q documentation
Enumerate is a q operator that returns one list as an enumeration of another.
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