2000-02-03：使各种节点的EXPLAIN结果更具说服力。
25 年前的今天（PostgreSQL 7.0 开发周期），一个补丁被提交，使 EXPLAIN 对于 Append、Group、Agg 和 Unique 节点的执行结果更加合理。
commit d24ef0d08fd278bbaa130329ff08de76f980b5aa Author: Tom Lane <tgl@sss.pgh.pa.us> Date: Thu Feb 3 06:12:19 2000 +0000 Make EXPLAIN results for Append, Group, Agg, Unique nodes more plausible. Group and Unique use an arbitrary assumption that there will be about 10% as many groups as input tuples --- perhaps someday we can refine this.