influxql doc.

docs/src/en/ecosystem/influxdb.md

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+# InfluxDB
+
+[InfluxDB](https://www.influxdata.com/products/influxdb-overview/) is a time series database designed to handle high write and query loads. It is an integral component of the TICK stack. InfluxDB is meant to be used as a backing store for any use case involving large amounts of timestamped data, including DevOps monitoring, application metrics, IoT sensor data, and real-time analytics.
+
+CeresDB support both write and query through [influxDB 1.x http api described in doc of influxDB 1.8](https://docs.influxdata.com/influxdb/v1.8/tools/api/#influxdb-1x-http-endpoints).
+
+## Write api
+
+Insert data by POST HTTP requests:
+
+```shell
+curl -i -XPOST "http://localhost:5440/influxdb/v1/write?db=public&precision=ms" --data-binary 'mymeas,mytag=1 myfield=90 1463683075'
+```
+
+- Body:
+
+  - Inserted data formatted by [line protocol](https://docs.influxdata.com/influxdb/v1.8/concepts/glossary/#influxdb-line-protocol).
+
+- Query parameters:
+
+  - `precision`, precision of timestamps in the line protocol, default to `ms`.
+  - `db`, not supported to set now.
+
+Measurement will be created automatically like what in influxDB, and each measurement will be mapped to a table.
+
+For example, when inserting data above, table as following will be created in CeresDB:
+
+```sql
+  CREATE TABLE `mymeas` (
+    `tsid` uint64 NOT NULL,
+    `timestamp` timestamp NOT NULL,
+    `myfield` double,
+    `mytag` string TAG,
+    PRIMARY KEY(tsid,timestamp), TIMESTAMP KEY(timestamp)
+  )
+```
+
+## Query api
+
+```shell
+ curl -G 'http://localhost:5440/influxdb/v1/query?db=public' --data-urlencode 'q=SELECT * FROM "mymeas"'
+```
+
+- Body:
+
+  - `q`, influxQL string to execute(when query by POST requests).
+
+- Query parameters:
+
+  - `q`, when query by GET requests, see also in body.
+  - `db`, `epoch`, `pretty`, `chunked` are not supported to set now.