[
https://issues.apache.org/jira/browse/CALCITE-4242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17197422#comment-17197422
]
Martin Raszyk commented on CALCITE-4242:
----------------------------------------
I tried to use `LEFT SEMI JOIN` in PostgreSQL version `psql (PostgreSQL) 12.4
(Ubuntu 12.4-0ubuntu0.20.04.1)`, but I didn't succeed.
The query
{code:java}
SELECT x FROM P LEFT SEMI JOIN Q ON TRUE;
{code}
leads to syntax error.
The query
{code:java}
SELECT x FROM P SEMI JOIN Q ON TRUE;
{code}
is evaluated, but does not yield the proper multiplicities.
Finally, the query
{code:java}
SELECT my_p.x FROM P AS my_p SEMI JOIN Q ON TRUE;
{code}
leads to syntax error, too.
Moreover, I said that "one could keep the LEFT JOIN right-associative for
nested NOT EXISTS subqueries *without data dependencies crossing two nesting
levels*". In my very original query
{code:java}
SELECT x FROM P
WHERE NOT EXISTS (
SELECT y FROM Q
WHERE NOT EXISTS (
SELECT z FROM R
WHERE x = z
)
)
{code}
this is not the case and your most recent query which I fixed as follows so
that it evaluates
{code:java}
WITH
q_present AS (SELECT TRUE as present FROM q),
r_present_given_z AS (SELECT TRUE as present, z FROM r GROUP BY z),
q_present_given_r_present_given_z AS (
SELECT TRUE AS present, r_present_given_z.present AS r_present,
r_present_given_z.z AS r_z
FROM q_present
LEFT JOIN r_present_given_z ON TRUE
)
SELECT my_p.x
FROM P my_p
LEFT JOIN q_present_given_r_present_given_z ON
q_present_given_r_present_given_z.r_z = my_p.x
WHERE NOT(
q_present_given_r_present_given_z.present
AND NOT q_present_given_r_present_given_z.r_present
);
{code}
is not equivalent to my very original query with the same counter-example as
you very first suggestion:
{code:java}
CREATE TABLE P(x INTEGER);
CREATE TABLE Q(y INTEGER);
CREATE TABLE R(z INTEGER);
INSERT INTO P VALUES (1);
{code}
> Wrong plan for nested NOT EXISTS subqueries
> -------------------------------------------
>
> Key: CALCITE-4242
> URL: https://issues.apache.org/jira/browse/CALCITE-4242
> Project: Calcite
> Issue Type: Bug
> Reporter: Martin Raszyk
> Priority: Major
>
> Suppose we initialize an empty database as follows.
>
> {code:java}
> CREATE TABLE P(x INTEGER);
> CREATE TABLE Q(y INTEGER);
> CREATE TABLE R(z INTEGER);
> INSERT INTO P VALUES (1);
> INSERT INTO Q VALUES (1);{code}
>
> The following query is supposed to yield an empty table as the result.
>
> {code:java}
> SELECT x FROM P
> WHERE NOT EXISTS (
> SELECT y FROM Q
> WHERE NOT EXISTS (
> SELECT z FROM R
> WHERE x = z
> )
> ){code}
>
> However, the query is parsed and converted to the following plan
> {code:java}
> LogicalProject(X=[$0])
> LogicalFilter(condition=[IS NULL($2)])
> LogicalJoin(condition=[=($0, $1)], joinType=[left])
> LogicalTableScan(table=[[Bug, P]])
> LogicalAggregate(group=[{0}], agg#0=[MIN($1)])
> LogicalProject(Z=[$1], $f0=[true])
> LogicalFilter(condition=[IS NULL($2)])
> LogicalJoin(condition=[true], joinType=[left])
> LogicalTableScan(table=[[Bug, Q]])
> LogicalAggregate(group=[{0}], agg#0=[MIN($1)])
> LogicalProject(Z=[$0], $f0=[true])
> LogicalTableScan(table=[[Bug, R]])
> {code}
> that corresponds to the following SQL query
> {code:java}
> SELECT P.X
> FROM Bug.P
> LEFT JOIN (SELECT t0.Z, MIN(TRUE) AS $f1
> FROM Bug.Q
> LEFT JOIN (SELECT Z, MIN(TRUE) AS $f1
> FROM Bug.R
> GROUP BY Z) AS t0 ON TRUE
> WHERE t0.$f1 IS NULL
> GROUP BY t0.Z) AS t3 ON P.X = t3.Z
> WHERE t3.$f1 IS NULL
> {code}
> which yields the (non-empty) table P as the result.
> Hence, the parsed and converted query is not equivalent to the input query.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
