docs(stream) (#18988)

docs/en/12-taos-sql/14-stream.md

@@ -10,7 +10,7 @@ Because stream processing is built in to TDengine, you are no longer reliant on
 ## Create a Stream
 
 ```sql
-CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name AS subquery
+CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name SUBTABLE(expression) AS subquery
 stream_options: {
  TRIGGER    [AT_ONCE | WINDOW_CLOSE | MAX_DELAY time]
  WATERMARK   time
@@ -30,6 +30,8 @@ subquery: SELECT [DISTINCT] select_list
 
 Session windows, state windows, and sliding windows are supported. When you configure a session or state window for a supertable, you must use PARTITION BY TBNAME.
 
+Subtable Clause defines the naming rules of auto-created subtable, you can see more details in below part: Partitions of Stream.
+
 ```sql
 window_clause: {
     SESSION(ts_col, tol_val)
@@ -47,6 +49,32 @@ CREATE STREAM avg_vol_s INTO avg_vol AS
 SELECT _wstart, count(*), avg(voltage) FROM meters PARTITION BY tbname INTERVAL(1m) SLIDING(30s);
 ```
 
+## Partitions of Stream
+
+A Stream can process data in multiple partitions. Partition rules can be defined by PARTITION BY clause in stream processing. Each partition will have different timelines and windows, and will be processed separately and be written into different subtables of target supertable.
+
+If a stream is created without PARTITION BY clause, all data will be written into one subtable.
+
+If a stream is created with PARTITION BY clause without SUBTABLE clause, each partition will be given a random name. 
+
+If a stream is created with PARTITION BY clause and SUBTABLE clause, the name of each partition will be calculated according to SUBTABLE clause. For example:
+
+```sql
+CREATE STREAM avg_vol_s INTO avg_vol SUBTABLE(CONCAT('new-', tname)) AS SELECT _wstart, count(*), avg(voltage) FROM meters PARTITION BY tbname tname INTERVAL(1m);
+```
+
+IN PARTITION clause, 'tbname', representing each subtable name of source supertable, is given alias 'tname'. And 'tname' is used in SUBTABLE clause. In SUBTABLE clause, each auto created subtable will concat 'new-' and source subtable name as their name. Other expressions are also allowed in SUBTABLE clause, but the output type must be varchar.
+
+If the output length exceeds the limitation of TDengine(192), the name will be truncated. If the generated name is occupied by some other table, the creation and writing of the new subtable will be failed.
+
+## Filling history data
+
+Normally a stream does not process data already or being written into source table when it's being creating. But adding FILL_HISTORY 1 as a stream option when creating the stream will allow it to process data written before and while creating the stream. For example:
+
+```sql
+create stream if not exists s1 fill_history 1 into st1  as select count(*) from t1 interval(10s)
+```
+
 ## Delete a Stream
 
 ```sql

docs/zh/12-taos-sql/14-stream.md

@@ -8,7 +8,7 @@ description: 流式计算的相关 SQL 的详细语法
 ## 创建流式计算
 
 ```sql
-CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name AS subquery
+CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name SUBTABLE(expression) AS subquery
 stream_options: {
  TRIGGER    [AT_ONCE | WINDOW_CLOSE | MAX_DELAY time]
  WATERMARK   time
@@ -28,6 +28,9 @@ subquery: SELECT select_list
 
 支持会话窗口、状态窗口与滑动窗口，其中，会话窗口与状态窗口搭配超级表时必须与partition by tbname一起使用
 
+
+subtable 子句定义了流式计算中创建的子表的命名规则，详见 流式计算的 partition 部分。
+
 ```sql
 window_clause: {
     SESSION(ts_col, tol_val)
@@ -49,11 +52,29 @@ SELECT _wstart, count(*), avg(voltage) FROM meters PARTITION BY tbname INTERVAL(
 
 ## 流式计算的 partition
 
-可以使用 PARTITION BY TBNAME 或 PARTITION BY tag，对一个流进行多分区的计算，每个分区的时间线与时间窗口是独立的，会各自聚合，并写入到目的表中的不同子表。
+可以使用 PARTITION BY TBNAME，tag，普通列或者表达式，对一个流进行多分区的计算，每个分区的时间线与时间窗口是独立的，会各自聚合，并写入到目的表中的不同子表。
+
+不带 PARTITION BY 子句时，所有的数据将写入到一张子表。
+
+在创建流时不使用 SUBTABLE 子句时，流式计算创建的超级表有唯一的 tag 列 groupId，每个 partition 会被分配唯一 groupId。与 schemaless 写入一致，我们通过 MD5 计算子表名，并自动创建它。
 
-不带 PARTITION BY 选项时，所有的数据将写入到一张子表。
+若创建流的语句中包含 SUBTABLE 子句，用户可以为每个 partition 对应的子表生成自定义的表名，例如：
+
+```sql
+CREATE STREAM avg_vol_s INTO avg_vol SUBTABLE(CONCAT('new-', tname)) AS SELECT _wstart, count(*), avg(voltage) FROM meters PARTITION BY tbname tname INTERVAL(1m);
+```
 
-流式计算创建的超级表有唯一的 tag 列 groupId，每个 partition 会被分配唯一 groupId。与 schemaless 写入一致，我们通过 MD5 计算子表名，并自动创建它。
+PARTITION 子句中，为 tbname 定义了一个别名 tname, 在PARTITION 子句中的别名可以用于 SUBTABLE 子句中的表达式计算，在上述示例中，流新创建的子表将以前缀 'new-' 连接原表名作为表名。
+
+注意，子表名的长度若超过 TDengine 的限制，将被截断。若要生成的子表名已经存在于另一超级表，由于 TDengine 的子表名是唯一的，因此对应新子表的创建以及数据的写入将会失败。
+
+## 流式计算读取历史数据
+
+正常情况下，流式计算不会处理创建前已经写入源表中的数据，若要处理已经写入的数据，可以在创建流时设置 fill_history 1 选项，这样创建的流式计算会自动处理创建前、创建中、创建后写入的数据。例如：
+
+```sql
+create stream if not exists s1 fill_history 1 into st1  as select count(*) from t1 interval(10s)
+```
 
 ## 删除流式计算