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https://issues.apache.org/jira/browse/CASSANDRA-19637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17847065#comment-17847065
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David Capwell commented on CASSANDRA-19637:
-------------------------------------------
I was curious so tried to run this in Accord to see what happens...
{code}
String cql = "BEGIN TRANSACTION\n" +
"LET a = (SELECT * FROM "+qualifiedTableName+" WHERE
k=?);\n" +
"SELECT a.v >= null;\n" +
"IF a.v >= null THEN\n" +
" INSERT INTO " + qualifiedTableName + "(k, v) VALUES
(?, ?);\n" +
"END IF\n" +
"COMMIT TRANSACTION";
{code}
* both the SELECT and the IF reject the syntax of a.v >= null, right now we use
"IS NULL" and "IS NOT NULL" here...
* SELECT doesn't allow "a.v IS NULL", so if you wish to know if your if block
was taken, then there isn't a way to do that in this case?
* when dropping the select and switching to "IS NULL", I had the following bind
values: 0, 0, []. When I query the table it returns [0, null]. // Empty and
Null look the same
* Testing out ">= []" ; select doesn't allow but IF does. The statement was
false as the row doesn't exist (null >= [] is false). When we add row [0, []]
we and change insert to do [0, [42]] the if statement is now true! a.v was
written as an empty list, so is it not "null" internally but instead byte[0]?
> LWT conditions on MultiCell collections return invalid results
> --------------------------------------------------------------
>
> Key: CASSANDRA-19637
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19637
> Project: Cassandra
> Issue Type: Bug
> Components: CQL/Semantics
> Reporter: Benjamin Lerer
> Assignee: Benjamin Lerer
> Priority: Normal
>
> Due to the way multicell collections are implemented, it is not possible to
> differentiate between {{null}} and empty collections like it is feasible for
> single cell (frozen) collections. Therefore an empty multicell collection
> will always be treated as {{null}}.
> Unfortunately, the way LWT conditions handle that is not consistent with that.
> For example for {{colA list<int>}} non null: {code}.. IF colA >= null{code}
> will throw an invalid request error whereas {code}..IF colA >= []{code} will
> returns {{true}}.
> Moreover, if we insert an empty list through:
> {code}INSERT INTO mytable (pk, colA) VALUES (1, []);{code}
> and use {code}DELETE FROM mytable WHERE pk=1 IF colA >= []{code} the returned
> results will be {code}{false, null}{code}. Which can be quite confusing.
> The way to fix that behaviour to make it consistent with other operations is
> to consider empty multicell collection input as {{null}} and reject the
> {{null}} input for non {{=}} and {{!=}} operators.
>
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