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If you create a temporary table in the session and try to join a columnstore table with it (with cross engine join enabled), then an error is returned:
MariaDB [test]> create table tc (id int, c1 char(3)) engine=columnstore;
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Query OK, 0 rows affected (0.74 sec)
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MariaDB [test]> insert into tc values (1, 'ABC');
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Query OK, 1 row affected (0.32 sec)
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MariaDB [test]> create temporary table tt (select id from tc where id < 10);
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Query OK, 1 row affected, 1 warning (0.02 sec)
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Records: 1 Duplicates: 0 Warnings: 1
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MariaDB [test]> select * from tc t1 join tt t2 on t1.id = t2.id;
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ERROR 1815 (HY000): Internal error: fatal error executing query in crossengine client lib(17)(17)
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MariaDB [test]>
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The reason for this is that the current architecture uses a separate connection to perform the non column store query. This is because it can support the tables not being local to the server the query is running on. To support this would require some re-architecture and limitations.
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