提交 c1b51872 编写于 作者: X Xiaoyu Wang

docs: fix query doc error

上级 5c86f820
......@@ -46,7 +46,7 @@ The following restrictions apply:
### Other Rules
- The window clause must occur after the PARTITION BY clause and before the GROUP BY clause. It cannot be used with a GROUP BY clause.
- The window clause must occur after the PARTITION BY clause. It cannot be used with a GROUP BY clause.
- SELECT clauses on windows can contain only the following expressions:
- Constants
- Aggregate functions
......@@ -78,7 +78,7 @@ These pseudocolumns occur after the aggregation clause.
1. A huge volume of interpolation output may be returned using `FILL`, so it's recommended to specify the time range when using `FILL`. The maximum number of interpolation values that can be returned in a single query is 10,000,000.
2. The result set is in ascending order of timestamp when you aggregate by time window.
3. If aggregate by window is used on STable, the aggregate function is performed on all the rows matching the filter conditions. If `PARTITION BY` is not used in the query, the result set will be returned in strict ascending order of timestamp; otherwise the result set is not exactly in the order of ascending timestamp in each group.
3. If aggregate by window is used on STable, the aggregate function is performed on all the rows matching the filter conditions. If `PARTITION BY` is not used in the query, the result set will be returned in strict ascending order of timestamp; otherwise the result set will be returned in the order of ascending timestamp in each group.
:::
......@@ -120,6 +120,12 @@ In case of using integer, bool, or string to represent the status of a device at
SELECT COUNT(*), FIRST(ts), status FROM temp_tb_1 STATE_WINDOW(status);
```
Only care about the information of the status window when the status is 2. For example:
```
SELECT * FROM (SELECT COUNT(*) AS cnt, FIRST(ts) AS fst, status FROM temp_tb_1 STATE_WINDOW(status)) t WHERE status = 2;
```
### Session Window
The primary key, i.e. timestamp, is used to determine which session window a row belongs to. As shown in the figure below, if the limit of time interval for the session window is specified as 12 seconds, then the 6 rows in the figure constitutes 2 time windows, [2019-04-28 14:22:10,2019-04-28 14:22:30] and [2019-04-28 14:23:10,2019-04-28 14:23:30] because the time difference between 2019-04-28 14:22:30 and 2019-04-28 14:23:10 is 40 seconds, which exceeds the time interval limit of 12 seconds.
......
......@@ -46,7 +46,7 @@ SELECT select_list FROM tb_name
### 窗口子句的规则
- 窗口子句位于数据切分子句之后,GROUP BY 子句之前,且不可以和 GROUP BY 子句一起使用。
- 窗口子句位于数据切分子句之后,不可以和 GROUP BY 子句一起使用。
- 窗口子句将数据按窗口进行切分,对每个窗口进行 SELECT 列表中的表达式的计算,SELECT 列表中的表达式只能包含:
- 常量。
- _wstart伪列、_wend伪列和_wduration伪列。
......@@ -71,7 +71,7 @@ FILL 语句指定某一窗口区间数据缺失的情况下的填充模式。填
1. 使用 FILL 语句的时候可能生成大量的填充输出,务必指定查询的时间区间。针对每次查询,系统可返回不超过 1 千万条具有插值的结果。
2. 在时间维度聚合中,返回的结果中时间序列严格单调递增。
3. 如果查询对象是超级表,则聚合函数会作用于该超级表下满足值过滤条件的所有表的数据。如果查询中没有使用 PARTITION BY 语句,则返回的结果按照时间序列严格单调递增;如果查询中使用了 PARTITION BY 语句分组,则返回结果中每个 PARTITION 内按照时间序列严格单调递增。
3. 如果查询对象是超级表,则聚合函数会作用于该超级表下满足值过滤条件的所有表的数据。如果查询中没有使用 PARTITION BY 语句,则返回的结果按照时间序列严格单调递增;如果查询中使用了 PARTITION BY 语句分组,则返回结果中每个 PARTITION 内按照时间序列严格单调递增。
:::
......@@ -113,6 +113,12 @@ SELECT COUNT(*) FROM temp_tb_1 INTERVAL(1m) SLIDING(2m);
SELECT COUNT(*), FIRST(ts), status FROM temp_tb_1 STATE_WINDOW(status);
```
仅关心 status 为 2 时的状态窗口的信息。例如:
```
SELECT * FROM (SELECT COUNT(*) AS cnt, FIRST(ts) AS fst, status FROM temp_tb_1 STATE_WINDOW(status)) t WHERE status = 2;
```
### 会话窗口
会话窗口根据记录的时间戳主键的值来确定是否属于同一个会话。如下图所示,如果设置时间戳的连续的间隔小于等于 12 秒,则以下 6 条记录构成 2 个会话窗口,分别是:[2019-04-28 14:22:10,2019-04-28 14:22:30]和[2019-04-28 14:23:10,2019-04-28 14:23:30]。因为 2019-04-28 14:22:30 与 2019-04-28 14:23:10 之间的时间间隔是 40 秒,超过了连续时间间隔(12 秒)。
......
Markdown is supported
0% .
You are about to add 0 people to the discussion. Proceed with caution.
先完成此消息的编辑!
想要评论请 注册