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查询结果集格式

在 IoTDB 中,查询结果集默认按照时间对齐,同时支持另外两种结果返回形式:

  • 设备时间对齐 align by device
  • 时序不对齐 disable align

注意:对齐方式子句只能用于查询语句句尾。

按设备对齐

align by device 对齐方式下,设备名会单独作为一列出现。如果 select 子句中有 n 列,最终结果就会有该 n + 2 列(时间列和设备名字列)。

SQL 形如:

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

结果如下:

+-----------------------------+-----------------+-----------+------+--------+
|                         Time|           Device|temperature|status|hardware|
+-----------------------------+-----------------+-----------+------+--------+
|2017-11-01T00:00:00.000+08:00|root.ln.wf01.wt01|      25.96|  true|    null|
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|      24.36|  true|    null|
|1970-01-01T08:00:00.001+08:00|root.ln.wf02.wt02|       null|  true|      v1|
|1970-01-01T08:00:00.002+08:00|root.ln.wf02.wt02|       null| false|      v2|
|2017-11-01T00:00:00.000+08:00|root.ln.wf02.wt02|       null|  true|      v2|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|       null|  true|      v2|
+-----------------------------+-----------------+-----------+------+--------+
Total line number = 6
It costs 0.012s

时序不对齐

disable align 对齐方式下,如果 select 子句中有 n 列,最终结果就会有该 n * 2 列(时间序列的时间和值)。

注:时序不对齐方式不能用于聚合查询、空值填充,但可使用 Limit 和 Offset 语句进行分页。

SQL 形如:

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

结果如下:

+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
|                         Time|root.ln.wf02.wt02.hardware|                         Time|root.ln.wf02.wt02.status|                         Time|root.ln.wf01.wt01.temperature|                         Time|root.ln.wf01.wt01.status|
+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
|1970-01-01T08:00:00.001+08:00|                        v1|1970-01-01T08:00:00.001+08:00|                    true|2017-11-01T00:00:00.000+08:00|                        25.96|2017-11-01T00:00:00.000+08:00|                    true|
|1970-01-01T08:00:00.002+08:00|                        v2|1970-01-01T08:00:00.002+08:00|                   false|2017-11-01T00:01:00.000+08:00|                        24.36|2017-11-01T00:01:00.000+08:00|                    true|
|2017-11-01T00:00:00.000+08:00|                        v2|2017-11-01T00:00:00.000+08:00|                    true|                         null|                         null|                         null|                    null|
|2017-11-01T00:01:00.000+08:00|                        v2|2017-11-01T00:01:00.000+08:00|                    true|                         null|                         null|                         null|                    null|
+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
Total line number = 4
It costs 0.018s

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