diff --git a/PostgreSQL/time.sql b/PostgreSQL/time.sql
index a7ee605..8ee4427 100644
--- a/PostgreSQL/time.sql
+++ b/PostgreSQL/time.sql
@@ -1,10 +1,10 @@
 -- 设置会话时区
 SET TIME ZONE 'Asia/Shanghai';
 
--- msg_time 是 timestamptz类型
-select msg_time from msg where id = 1;
-select msg_time AT TIME ZONE 'Asia/Shanghai' from msg where id = 1;
-select msg_time AT TIME ZONE 'UTC+8' from msg where id = 1;
+-- AT TIME ZONE 在 PostgreSQL 中是重载的，行为取决于左侧的类型：
+-- timestamp WITHOUT time zone AT TIME ZONE zone → 把该 wall time 视为 zone 的本地时间，然后转换为 UTC，结果为 timestamptz（显示为 UTC 偏移后的时间）。
+-- timestamptz AT TIME ZONE zone → 把该瞬间转换成 zone 的本地 wall time，结果为 timestamp WITHOUT time zone。
+select msg_time at time zone 'Asia/Shanghai' from msg where id = 1;
+select msg_time at time zone 'UTC+8' from msg where id = 1;
 
-SELECT to_timestamp(1761850339);
-SELECT to_timestamp(1761850339) AT TIME ZONE 'Asia/Shanghai';
+select to_timestamp(1761850339) AT TIME ZONE 'Asia/Shanghai';