In IoTDB, SELECT
statement is used to retrieve data from one or more selected time series. Here is the syntax definition of SELECT
statement:
[TRACING] SELECT [LAST] [TOP k] resultColumn [, resultColumn] ... FROM prefixPath [, prefixPath] ... WHERE whereCondition [GROUP BY ([startTime, endTime), interval, slidingStep)] [GROUP BY LEVEL = levelNum [, levelNum] ...] [FILL ({PREVIOUS, beforeRange | LINEAR, beforeRange, afterRange | constant})] [LIMIT rowLimit] [OFFSET rowOffset] [SLIMIT seriesLimit] [SOFFSET seriesOffset] [WITHOUT NULL {ANY | ALL} [resultColumn [, resultColumn] ...]] [ORDER BY TIME {ASC | DESC}] [{ALIGN BY DEVICE | DISABLE ALIGN}]
The most commonly used clauses of SELECT
statements are these:
resultColumn
indicates a column that you want to retrieve, which may be a suffix of time series paths, an aggregate function and so on. There must be at least one resultColumn
. For more details for resultColumn
, please refer to Select Expression .fromClause
contains the prefix of one or more time-series paths to query.whereCondition
(Optional) specify the filter criterion named queryfilter
. queryfilter
is a logical expression that returns the data points which calculation result is TRUE. If you do not specify whereCondition
, return all data points in the time series. For more details, please refer to Query Filter.ORDER BY TIME DESC
clause.LIMIT/SLIMIT
and OFFSET/SOFFSET
to paginate the result set, see Query Result Pagination for details.The SQL statement is:
select temperature from root.ln.wf01.wt01 where time < 2017-11-01T00:08:00.000
which means:
The selected device is ln group wf01 plant wt01 device; the selected timeseries is the temperature sensor (temperature). The SQL statement requires that all temperature sensor values before the time point of “2017-11-01T00:08:00.000” be selected.
The execution result of this SQL statement is as follows:
+-----------------------------+-----------------------------+ | Time|root.ln.wf01.wt01.temperature| +-----------------------------+-----------------------------+ |2017-11-01T00:00:00.000+08:00| 25.96| |2017-11-01T00:01:00.000+08:00| 24.36| |2017-11-01T00:02:00.000+08:00| 20.09| |2017-11-01T00:03:00.000+08:00| 20.18| |2017-11-01T00:04:00.000+08:00| 21.13| |2017-11-01T00:05:00.000+08:00| 22.72| |2017-11-01T00:06:00.000+08:00| 20.71| |2017-11-01T00:07:00.000+08:00| 21.45| +-----------------------------+-----------------------------+ Total line number = 8 It costs 0.026s
The SQL statement is:
select status, temperature from root.ln.wf01.wt01 where time > 2017-11-01T00:05:00.000 and time < 2017-11-01T00:12:00.000;
which means:
The selected device is ln group wf01 plant wt01 device; the selected timeseries is “status” and “temperature”. The SQL statement requires that the status and temperature sensor values between the time point of “2017-11-01T00:05:00.000” and “2017-11-01T00:12:00.000” be selected.
The execution result of this SQL statement is as follows:
+-----------------------------+------------------------+-----------------------------+ | Time|root.ln.wf01.wt01.status|root.ln.wf01.wt01.temperature| +-----------------------------+------------------------+-----------------------------+ |2017-11-01T00:06:00.000+08:00| false| 20.71| |2017-11-01T00:07:00.000+08:00| false| 21.45| |2017-11-01T00:08:00.000+08:00| false| 22.58| |2017-11-01T00:09:00.000+08:00| false| 20.98| |2017-11-01T00:10:00.000+08:00| true| 25.52| |2017-11-01T00:11:00.000+08:00| false| 22.91| +-----------------------------+------------------------+-----------------------------+ Total line number = 6 It costs 0.018s
IoTDB supports specifying multiple time interval conditions in a query. Users can combine time interval conditions at will according to their needs. For example, the SQL statement is:
select status,temperature from root.ln.wf01.wt01 where (time > 2017-11-01T00:05:00.000 and time < 2017-11-01T00:12:00.000) or (time >= 2017-11-01T16:35:00.000 and time <= 2017-11-01T16:37:00.000);
which means:
The selected device is ln group wf01 plant wt01 device; the selected timeseries is “status” and “temperature”; the statement specifies two different time intervals, namely “2017-11-01T00:05:00.000 to 2017-11-01T00:12:00.000” and “2017-11-01T16:35:00.000 to 2017-11-01T16:37:00.000”. The SQL statement requires that the values of selected timeseries satisfying any time interval be selected.
The execution result of this SQL statement is as follows:
+-----------------------------+------------------------+-----------------------------+ | Time|root.ln.wf01.wt01.status|root.ln.wf01.wt01.temperature| +-----------------------------+------------------------+-----------------------------+ |2017-11-01T00:06:00.000+08:00| false| 20.71| |2017-11-01T00:07:00.000+08:00| false| 21.45| |2017-11-01T00:08:00.000+08:00| false| 22.58| |2017-11-01T00:09:00.000+08:00| false| 20.98| |2017-11-01T00:10:00.000+08:00| true| 25.52| |2017-11-01T00:11:00.000+08:00| false| 22.91| |2017-11-01T16:35:00.000+08:00| true| 23.44| |2017-11-01T16:36:00.000+08:00| false| 21.98| |2017-11-01T16:37:00.000+08:00| false| 21.93| +-----------------------------+------------------------+-----------------------------+ Total line number = 9 It costs 0.018s
The system supports the selection of data in any column in a query, i.e., the selected columns can come from different devices. For example, the SQL statement is:
select wf01.wt01.status,wf02.wt02.hardware from root.ln where (time > 2017-11-01T00:05:00.000 and time < 2017-11-01T00:12:00.000) or (time >= 2017-11-01T16:35:00.000 and time <= 2017-11-01T16:37:00.000);
which means:
The selected timeseries are “the power supply status of ln group wf01 plant wt01 device” and “the hardware version of ln group wf02 plant wt02 device”; the statement specifies two different time intervals, namely “2017-11-01T00:05:00.000 to 2017-11-01T00:12:00.000” and “2017-11-01T16:35:00.000 to 2017-11-01T16:37:00.000”. The SQL statement requires that the values of selected timeseries satisfying any time interval be selected.
The execution result of this SQL statement is as follows:
+-----------------------------+------------------------+--------------------------+ | Time|root.ln.wf01.wt01.status|root.ln.wf02.wt02.hardware| +-----------------------------+------------------------+--------------------------+ |2017-11-01T00:06:00.000+08:00| false| v1| |2017-11-01T00:07:00.000+08:00| false| v1| |2017-11-01T00:08:00.000+08:00| false| v1| |2017-11-01T00:09:00.000+08:00| false| v1| |2017-11-01T00:10:00.000+08:00| true| v2| |2017-11-01T00:11:00.000+08:00| false| v1| |2017-11-01T16:35:00.000+08:00| true| v2| |2017-11-01T16:36:00.000+08:00| false| v1| |2017-11-01T16:37:00.000+08:00| false| v1| +-----------------------------+------------------------+--------------------------+ Total line number = 9 It costs 0.014s
IoTDB supports the ‘order by time’ statement since 0.11, it's used to display results in descending order by time. For example, the SQL statement is:
select * from root.ln.** where time > 1 order by time desc limit 10;
The execution result of this SQL statement is as follows:
+-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+ | Time|root.ln.wf02.wt02.hardware|root.ln.wf02.wt02.status|root.ln.wf01.wt01.temperature|root.ln.wf01.wt01.status| +-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+ |2017-11-07T23:59:00.000+08:00| v1| false| 21.07| false| |2017-11-07T23:58:00.000+08:00| v1| false| 22.93| false| |2017-11-07T23:57:00.000+08:00| v2| true| 24.39| true| |2017-11-07T23:56:00.000+08:00| v2| true| 24.44| true| |2017-11-07T23:55:00.000+08:00| v2| true| 25.9| true| |2017-11-07T23:54:00.000+08:00| v1| false| 22.52| false| |2017-11-07T23:53:00.000+08:00| v2| true| 24.58| true| |2017-11-07T23:52:00.000+08:00| v1| false| 20.18| false| |2017-11-07T23:51:00.000+08:00| v1| false| 22.24| false| |2017-11-07T23:50:00.000+08:00| v2| true| 23.7| true| +-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+ Total line number = 10 It costs 0.016s
Data query statements can be used in SQL command-line terminals, JDBC, JAVA / C++ / Python / Go and other native APIs, and RESTful APIs.
Execute the query statement in the SQL command line terminal: start the SQL command line terminal, and directly enter the query statement to execute, see SQL command line terminal.
Execute query statements in JDBC, see JDBC for details.
Execute query statements in native APIs such as JAVA / C++ / Python / Go. For details, please refer to the relevant documentation in the Application Programming Interface chapter. The interface prototype is as follows:
SessionDataSet executeQueryStatement(String sql)
Used in RESTful API, see HTTP API for details.