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https://issues.apache.org/jira/browse/DERBY-2374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770717#action_12770717
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Dag H. Wanvik commented on DERBY-2374:
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Could this is a heuristic made necessary by the LL(n) nature of the
parser (recursive descent)? I think the parser can't really know
whether it's seeing seeing a "( <table reference ... " or a "( <query
expression body.." without looking past the matching ")" +
correlation and seeing a join operator or not.
- If it does see a join operator there, it should descend into <table
reference>)
- If is does *not* see a join operator there, it should descend into
<query expression body>, i.e. a subquery, which it failed to do here.
I suspect this long back-ahead + paren matching may be beyong JavaCC..
So, the authors of this code found a workable heuristic, which fails in
this case :( Maybe there is a way to finesse it, though..
> UNION PROBLEM WITH PARENTHESIS
> ------------------------------
>
> Key: DERBY-2374
> URL: https://issues.apache.org/jira/browse/DERBY-2374
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.1.3.3, 10.2.2.0, 10.3.3.1, 10.4.2.1, 10.5.3.1,
> 10.6.0.0
> Reporter: Kenneth Gee
> Priority: Minor
>
> The following query shows the error using the Derby demo toursDB:
> SELECT FLIGHT_ID , SEGMENT_NUMBER , ARRIVE_TIME
> FROM (
> (SELECT HW.FLIGHT_ID , HW.SEGMENT_NUMBER , HW.ARRIVE_TIME FROM
> FLIGHTS HW)
> UNION
> (SELECT SW.FLIGHT_ID , SW.SEGMENT_NUMBER , SW.ARRIVE_TIME FROM
> FLIGHTS SW)
> ) SRC;
> ERROR 42X01: Syntax error: Encountered "UNION" at line 4, column 12.
> The following query works:
> SELECT FLIGHT_ID , SEGMENT_NUMBER , ARRIVE_TIME
> FROM (
> SELECT HW.FLIGHT_ID , HW.SEGMENT_NUMBER , HW.ARRIVE_TIME FROM
> FLIGHTS HW
> UNION
> SELECT SW.FLIGHT_ID , SW.SEGMENT_NUMBER , SW.ARRIVE_TIME FROM
> FLIGHTS SW
> ) SRC;
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