- `INTERP` is used to get the value that matches the specified time slice from a column. If no such value exists an interpolation value will be returned based on `FILL` parameter.
- The input data of `INTERP` is the value of the specified column and a `where` clause can be used to filter the original data. If no `where` condition is specified then all original data is the input.
- `INTERP` must be used along with `RANGE`, `EVERY`, `FILL` keywords.
- The output time range of `INTERP` is specified by `RANGE(timestamp1,timestamp2)` parameter, with timestamp1<=timestamp2. timestamp1 is the starting point of the output time range and must be specified. timestamp2 is the ending point of the output time range and must be specified.
- The number of rows in the result set of `INTERP` is determined by the parameter `EVERY`. Starting from timestamp1, one interpolation is performed for every time interval specified `EVERY` parameter. The parameter `EVERY` must be an integer, with no quotes, with a time unit of: b(nanosecond), u(microsecond), a(millisecond)), s(second), m(minute), h(hour), d(day), or w(week). For example, `EVERY(500a)` will interpolate every 500 milliseconds.
- Interpolation is performed based on `FILL` parameter.
@@ -269,10 +269,10 @@ CREATE TOPIC topic_name AS STABLE stb_name
语法:
```sql
CREATE TOPIC topic_name [WITH META] AS DATABASE db_name;
CREATE TOPIC topic_name AS DATABASE db_name;
```
通过该语句可创建一个包含数据库所有表数据的订阅,`WITH META` 可选择将数据库结构变动信息加入到订阅消息流,TMQ 将消费当前数据库下所有表结构的变动,包括超级表的创建与删除,列添加、删除或修改,子表的创建、删除及 TAG 变动信息等等。消费者可通过 API 来判断具体的消息类型。这一点也是与 Kafka 不同的地方。