docs(stream): document streaming computation support for virtual tables in user manual (#30319)

* docs(stream): document streaming computation support for virtual tables in user manual

- Added section to user manual describing streaming computation support for virtual tables
- Listed known limitations and behavior when using virtual tables in streaming mode

* Update 14-stream.md

---------

Co-authored-by: Pan Wei <72057773+dapan1121@users.noreply.github.com>

docs/en/14-reference/03-taos-sql/14-stream.md

@@ -532,6 +532,24 @@ These fields are present only when "windowType" is "Count".
 #### Fields for Window Invalidation
 
 Due to scenarios such as data disorder, updates, or deletions during stream computing, windows that have already been generated might be removed or their results need to be recalculated. In such cases, a notification with the eventType "WINDOW_INVALIDATION" is sent to inform which windows have been invalidated.
+
 For events with "eventType" as "WINDOW_INVALIDATION", the following fields are included:
 1. "windowStart": A long integer timestamp representing the start time of the window.
 1. "windowEnd": A long integer timestamp representing the end time of the window.
+
+## Support for Virtual Tables in Stream Computing
+
+Starting with v3.3.6.0, stream computing can use virtual tables—including virtual regular tables, virtual sub-tables, and virtual super tables—as data sources for computation. The syntax is identical to that for non‑virtual tables.
+
+However, because the behavior of virtual tables differs from that of non‑virtual tables, the following restrictions apply when using stream computing:
+
+1. The schema of virtual regular tables/virtual sub-tables involved in stream computing cannot be modified.
+1. During stream computing, if the data source corresponding to a column in a virtual table is changed, the stream computation will not pick up the change; it will still read from the old data source.
+1. During stream computing, if the original table corresponding to a column in a virtual table is deleted and later a new table with the same name and a column with the same name is created, the stream computation will not read data from the new table.
+1. The watermark for stream computing must be 0; otherwise, an error will occur during creation.
+1. If the data source for stream computing is a virtual super table, sub-tables that are added after the stream computing task starts will not participate in the computation.
+1. The timestamps of different underlying tables in a virtual table may not be completely consistent; merging the data might produce null values, and interpolation is currently not supported.
+1. Out-of-order data, updates, or deletions are not handled. In other words, when creating a stream, you cannot specify `ignore update 0` or `ignore expired 0`; otherwise, an error will be reported.
+1. Historical data computation is not supported. That is, when creating a stream, you cannot specify `fill_history 1`; otherwise, an error will be reported.
+1. The trigger modes MAX_DELAY, CONTINUOUS_WINDOW_CLOSE and FORCE_WINDOW_CLOSE are not supported.
+1. The COUNT_WINDOW type is not supported.

docs/zh/14-reference/03-taos-sql/14-stream.md

@@ -527,6 +527,24 @@ CREATE STREAM avg_current_stream FILL_HISTORY 1
 #### 窗口失效相关字段
 
 因为流计算过程中会遇到数据乱序、更新、删除等情况，可能造成已生成的窗口被删除，或者结果需要重新计算。此时会向通知地址发送一条 WINDOW_INVALIDATION 的通知，说明哪些窗口已经被删除。
+
 这部分是 eventType 为 WINDOW_INVALIDATION 时，event 对象才有的字段。
 1. windowStart：长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
 1. windowEnd: 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
+
+## 流式计算对虚拟表的支持
+
+从 v3.3.6.0 开始，流计算能够使用虚拟表（包括虚拟普通表、虚拟子表、虚拟超级表）作为数据源进行计算，语法和非虚拟表完全一致。
+
+但是虚拟表的行为与非虚拟表存在差异，所以目前在使用流计算对虚拟表进行计算时存在以下限制：
+
+1. 流计算中涉及的虚拟普通表/虚拟子表的 schema 不允许更改。
+1. 流计算过程中，如果修改虚拟表某一列对应的数据源，对流计算来说不生效。即：流计算仍只读取老的数据源。
+1. 流计算过程中，如果虚拟表某一列对应的原始表被删除，之后新建了同名的表和同名的列，流计算不会读取新表的数据。
+1. 流计算的 watermark 只能是 0，否则创建时就报错。
+1. 如果流计算的数据源是虚拟超级表，流计算任务启动后新增的子表不参与计算。
+1. 虚拟表的不同原始表的时间戳不完全一致，数据合并后可能会产生空值，暂不支持插值处理。
+1. 不处理数据的乱序、更新或删除。即：流创建时不能指定 `ignore update 0` 或者 `ignore expired 0`，否则报错。
+1. 不支持历史数据计算，即：流创建时不能指定 `fill_history 1`，否则报错。
+1. 不支持触发模式：MAX_DELAY, FORCE_WINDOW_CLOSE, CONTINUOUS_WINDOW_CLOSE。
+1. 不支持窗口类型：COUNT_WINDOW。