subquery_to_derived duplicate name

With optimizer_switch='subquery_to_derived=on', running the reproducer below on a freshly created schema crashes the server process. The query was expected to return a result set (or at worst a query-level error) without affecting the server, but instead the server crashes. With subquery_to_derived=off the same query runs fine.

Crash SQL

CREATE TABLE t1 (a BIGINT PRIMARY KEY, b BIGINT);
CREATE TABLE t2 (a BIGINT PRIMARY KEY);

SELECT /*+ SET_VAR(optimizer_switch='subquery_to_derived=on') */
       COUNT(DISTINCT s.a) = (SELECT COUNT(DISTINCT s1.a)
                              FROM t2 s1 WHERE s1.a = o.b) AS x
FROM t1 o LEFT JOIN t2 s ON o.b = s.a
GROUP BY o.a, o.b;

首先，在启用 subquery_to_derived 的全新创建的 schema 上运行提供的 SQL 复现程序，然后将其与禁用该设置的情况进行比较。跟踪转换子查询并处理重复名称的优化器路径；完成的标准是查询不再导致服务器崩溃，而是返回结果集或查询级错误。