From: Elvis Pranskevichus <elprans@gmail.com>
To: pgsql-bugs@postgresql.org
Subject: ERROR:  could not devise a query plan for the given query (UNIONS and
 LATERAL)
Date: Tue, 23 Jan 2018 13:10:59 -0500
Message-ID: <5981018.zdth1YWmNy@hammer.magicstack.net>
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Hi,

The following (admittedly bizzare) query causes the error in the subject 
on all recent versions of Postgres:

SELECT
        "q2"."v"
    FROM
        LATERAL
        (SELECT
                "q11"."v"
            FROM
                (
                    (SELECT 2::bigint AS "v") UNION ALL
                    (SELECT 3::bigint AS "v")
                ) AS "q11"
        ) AS "q1"
        CROSS JOIN LATERAL
        (
            (SELECT
                "q3"."v"
             FROM
                (
                    (SELECT 4::bigint AS "v") UNION ALL
                    (SELECT 5::bigint AS "v")
                ) AS "q3"
            )
            UNION ALL
            (SELECT "q1"."v")
        ) AS "q2"
    ORDER BY
        "q2"."v"; 


Interestingly, removing UNION from either "q3" or "q11", as well as 
removing the ::bigint casts makes it work.


                            Elvis