Possible mem leak and crash in columnstore's mysqld

There's a data item in lex called result, a pointer to a select_result item. This is created and set by parse_sql().

During columnstore processing, we run parse_sql multiple times, throwing away the result object. Not deleteing – throwing away.

When certain queries are sent via pipe to the client, the result item isn't thrown away and an assert happens. I believe we throw it away in most processing just to avoid the assert, but it needs to be cleaned up instead.

Put the following query into a file and pipe it to the client to cause the assert:

select lo_orderkey into outfile '/tmp/bug3520.txt' from (select lo_orderkey from lineorder group by 1 union all select lo_orderkey from lineorder group by 1 union all select lo_orderkey from lineorder group by 1 union all select lo_orderkey from lineorder group by 1 union all select lo_orderkey from lineorder group by 1) x;