docs(query): enhance time window clause descriptions in the documentation

docs/en/05-basic/03-query.md

@@ -191,7 +191,7 @@ INTERVAL(interval_val [, interval_offset])
 
 The time window clause includes 3 sub-clauses:
 
-- INTERVAL clause: used to generate windows of equal time periods, where interval_val specifies the size of each time window, and interval_offset specifies;
+- INTERVAL clause: used to generate windows of equal time periods, where interval_val specifies the size of each time window, and interval_offset specifies its starting offset. By default, windows begin at Unix time 0 (1970-01-01 00:00:00 UTC). If interval_offset is specified, the windows start from "Unix time 0 + interval_offset";
 - SLIDING clause: used to specify the time the window slides forward;
 - FILL: used to specify the filling mode of data in case of missing data in the window interval.
 

docs/en/14-reference/03-taos-sql/12-distinguished.md

@@ -112,7 +112,7 @@ The differences between NULL, NULL_F, VALUE, VALUE_F filling modes for different
 
 Time windows can be divided into sliding time windows and tumbling time windows.
 
-The INTERVAL clause is used to generate windows of equal time periods, and SLIDING is used to specify the time the window slides forward. Each executed query is a time window, and the time window slides forward as time flows. When defining continuous queries, it is necessary to specify the size of the time window (time window) and the forward sliding times for each execution. As shown, [t0s, t0e], [t1s, t1e], [t2s, t2e] are the time window ranges for three continuous queries, and the sliding time range is indicated by sliding time. Query filtering, aggregation, and other operations are performed independently for each time window. When SLIDING is equal to INTERVAL, the sliding window becomes a tumbling window.
+The INTERVAL clause is used to generate windows of equal time periods, and SLIDING is used to specify the time the window slides forward. Each executed query is a time window, and the time window slides forward as time flows. When defining continuous queries, it is necessary to specify the size of the time window (time window) and the forward sliding times for each execution. As shown, [t0s, t0e], [t1s, t1e], [t2s, t2e] are the time window ranges for three continuous queries, and the sliding time range is indicated by sliding time. Query filtering, aggregation, and other operations are performed independently for each time window. When SLIDING is equal to INTERVAL, the sliding window becomes a tumbling window. By default, windows begin at Unix time 0 (1970-01-01 00:00:00 UTC). If interval_offset is specified, the windows start from "Unix time 0 + interval_offset".
 
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docs/zh/05-basic/03-query.md

@@ -182,7 +182,7 @@ INTERVAL(interval_val [, interval_offset])
 ```
 
 时间窗口子句包括 3 个子句：
-- INTERVAL 子句：用于产生相等时间周期的窗口，interval_val 指定每个时间窗口的大小，interval_offset 指定窗口偏移量；
+- INTERVAL 子句：用于产生相等时间周期的窗口，interval_val 指定每个时间窗口的大小，interval_offset 指定窗口偏移量；默认情况下，窗口是从 Unix time 0（1970-01-01 00:00:00 UTC）开始划分的；如果设置了 interval_offset，那么窗口的划分将从 “Unix time 0 + interval_offset” 开始；
 - SLIDING 子句：用于指定窗口向前滑动的时间；
 - FILL：用于指定窗口区间数据缺失的情况下，数据的填充模式。
 
@@ -688,4 +688,4 @@ select a.* from meters a left asof join meters b on timetruncate(a.ts, 1s) < tim
 
 查询结果顺序的限制包括如下这些。
 - 普通表、子表、subquery 且无分组条件无排序的场景下，查询结果会按照驱动表的主键列顺序输出。
-- 由于超级表查询、Full Join 或有分组条件无排序的场景下，查询结果没有固定的输出顺序，因此，在有排序需求且输出无固定顺序的场景下，需要进行排序操作。部分依赖时间线的函数可能会因为没有有效的时间线输出而无法执行。
+- 由于超级表查询、Full Join 或有分组条件无排序的场景下，查询结果没有固定的输出顺序，因此，在有排序需求且输出无固定顺序的场景下，需要进行排序操作。部分依赖时间线的函数可能会因为没有有效的时间线输出而无法执行。

docs/zh/14-reference/03-taos-sql/12-distinguished.md

@@ -104,7 +104,7 @@ NULL、NULL_F、VALUE、 VALUE_F 这几种填充模式针对不同场景区别
 
 时间窗口又可分为滑动时间窗口和翻转时间窗口。
 
-INTERVAL 子句用于产生相等时间周期的窗口，SLIDING 用以指定窗口向前滑动的时间。每次执行的查询是一个时间窗口，时间窗口随着时间流动向前滑动。在定义连续查询的时候需要指定时间窗口（time window ）大小和每次前向增量时间（forward sliding times）。如图，[t0s, t0e] ，[t1s , t1e]，[t2s, t2e] 是分别是执行三次连续查询的时间窗口范围，窗口的前向滑动的时间范围 sliding time 标识 。查询过滤、聚合等操作按照每个时间窗口为独立的单位执行。当 SLIDING 与 INTERVAL 相等的时候，滑动窗口即为翻转窗口。
+INTERVAL 子句用于产生相等时间周期的窗口，SLIDING 用以指定窗口向前滑动的时间。每次执行的查询是一个时间窗口，时间窗口随着时间流动向前滑动。在定义连续查询的时候需要指定时间窗口（time window ）大小和每次前向增量时间（forward sliding times）。如图，[t0s, t0e] ，[t1s , t1e]，[t2s, t2e] 是分别是执行三次连续查询的时间窗口范围，窗口的前向滑动的时间范围 sliding time 标识 。查询过滤、聚合等操作按照每个时间窗口为独立的单位执行。当 SLIDING 与 INTERVAL 相等的时候，滑动窗口即为翻转窗口。默认情况下，窗口是从 Unix time 0（1970-01-01 00:00:00 UTC）开始划分的；如果设置了 interval_offset，那么窗口的划分将从 “Unix time 0 + interval_offset” 开始。
 
 ![TDengine Database 时间窗口示意图](./timewindow-1.webp)