Order By

order by in ALIGN BY TIME mode

The result set of IoTDB is in ALIGN BY TIME mode by default and ORDER BY TIME clause can also be used to specify the ordering of timestamp. The SQL statement is:

select * from root.ln.** where time <= 2017-11-01T00:01:00 order by time desc;

执行结果：

+-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+
|                         Time|root.ln.wf02.wt02.hardware|root.ln.wf02.wt02.status|root.ln.wf01.wt01.temperature|root.ln.wf01.wt01.status|
+-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+
|2017-11-01T00:01:00.000+08:00|                        v2|                    true|                        24.36|                    true|
|2017-11-01T00:00:00.000+08:00|                        v2|                    true|                        25.96|                    true|
|1970-01-01T08:00:00.002+08:00|                        v2|                   false|                         null|                    null|
|1970-01-01T08:00:00.001+08:00|                        v1|                    true|                         null|                    null|
+-----------------------------+--------------------------+------------------------+-----------------------------+------------------------+
Total line number = 4

order by in ALIGN BY DEVICE mode

When querying in ALIGN BY DEVICE mode, ORDER BY clause can be used to specify the ordering of result set.

ALIGN BY DEVICE mode supports four kinds of clauses with two sort keys which are Device and Time.

1. ORDER BY DEVICE: sort by the alphabetical order of the device name. The devices with the same column names will be clustered in a group view.

2. ORDER BY TIME: sort by the timestamp, the data points from different devices will be shuffled according to the timestamp.

3. ORDER BY DEVICE,TIME: sort by the alphabetical order of the device name. The data points with the same device name will be sorted by timestamp.

4. ORDER BY TIME,DEVICE: sort by timestamp. The data points with the same time will be sorted by the alphabetical order of the device name.

To make the result set more legible, when ORDER BY clause is not used, default settings will be provided.
The default ordering clause is ORDER BY DEVICE,TIME and the default ordering is ASC.

When Device is the main sort key, the result set is sorted by device name first, then by timestamp in the group with the same device name, the SQL statement is:

select * from root.ln.** where time <= 2017-11-01T00:01:00 order by device desc,time asc align by device;

The result shows below:

+-----------------------------+-----------------+--------+------+-----------+
|                         Time|           Device|hardware|status|temperature|
+-----------------------------+-----------------+--------+------+-----------+
|1970-01-01T08:00:00.001+08:00|root.ln.wf02.wt02|      v1|  true|       null|
|1970-01-01T08:00:00.002+08:00|root.ln.wf02.wt02|      v2| false|       null|
|2017-11-01T00:00:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
|2017-11-01T00:00:00.000+08:00|root.ln.wf01.wt01|    null|  true|      25.96|
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|    null|  true|      24.36|
+-----------------------------+-----------------+--------+------+-----------+
Total line number = 6

When Time is the main sort key, the result set is sorted by timestamp first, then by device name in data points with the same timestamp. The SQL statement is:

select * from root.ln.** where time <= 2017-11-01T00:01:00 order by time asc,device desc align by device;

The result shows below:

+-----------------------------+-----------------+--------+------+-----------+
|                         Time|           Device|hardware|status|temperature|
+-----------------------------+-----------------+--------+------+-----------+
|1970-01-01T08:00:00.001+08:00|root.ln.wf02.wt02|      v1|  true|       null|
|1970-01-01T08:00:00.002+08:00|root.ln.wf02.wt02|      v2| false|       null|
|2017-11-01T00:00:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
|2017-11-01T00:00:00.000+08:00|root.ln.wf01.wt01|    null|  true|      25.96|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|    null|  true|      24.36|
+-----------------------------+-----------------+--------+------+-----------+
Total line number = 6

When ORDER BY clause is not used, sort in default way, the SQL statement is：

select * from root.ln.** where time <= 2017-11-01T00:01:00 align by device;

The result below indicates ORDER BY DEVICE ASC,TIME ASC is the clause in default situation.
ASC can be omitted because it's the default ordering.

+-----------------------------+-----------------+--------+------+-----------+
|                         Time|           Device|hardware|status|temperature|
+-----------------------------+-----------------+--------+------+-----------+
|2017-11-01T00:00:00.000+08:00|root.ln.wf01.wt01|    null|  true|      25.96|
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|    null|  true|      24.36|
|1970-01-01T08:00:00.001+08:00|root.ln.wf02.wt02|      v1|  true|       null|
|1970-01-01T08:00:00.002+08:00|root.ln.wf02.wt02|      v2| false|       null|
|2017-11-01T00:00:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|      v2|  true|       null|
+-----------------------------+-----------------+--------+------+-----------+
Total line number = 6

Besides，ALIGN BY DEVICE and ORDER BY clauses can be used with aggregate query，the SQL statement is：

select count(*) from root.ln.** group by ((2017-11-01T00:00:00.000+08:00,2017-11-01T00:03:00.000+08:00],1m) order by device asc,time asc align by device

The result shows below:

+-----------------------------+-----------------+---------------+-------------+------------------+
|                         Time|           Device|count(hardware)|count(status)|count(temperature)|
+-----------------------------+-----------------+---------------+-------------+------------------+
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|           null|            1|                 1|
|2017-11-01T00:02:00.000+08:00|root.ln.wf01.wt01|           null|            0|                 0|
|2017-11-01T00:03:00.000+08:00|root.ln.wf01.wt01|           null|            0|                 0|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|              1|            1|              null|
|2017-11-01T00:02:00.000+08:00|root.ln.wf02.wt02|              0|            0|              null|
|2017-11-01T00:03:00.000+08:00|root.ln.wf02.wt02|              0|            0|              null|
+-----------------------------+-----------------+---------------+-------------+------------------+
Total line number = 6