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选择函数

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选择函数

目前 IoTDB 支持如下选择函数:

函数名输入序列类型必要的属性参数输出序列类型功能描述
TOP_KINT32 / INT64 / FLOAT / DOUBLE / TEXTk: 最多选择的数据点数,必须大于 0 小于等于 1000与输入序列的实际类型一致返回某时间序列中值最大的k个数据点。若多于k个数据点的值并列最大,则返回时间戳最小的数据点。
BOTTOM_KINT32 / INT64 / FLOAT / DOUBLE / TEXTk: 最多选择的数据点数,必须大于 0 小于等于 1000与输入序列的实际类型一致返回某时间序列中值最小的k个数据点。若多于k个数据点的值并列最小,则返回时间戳最小的数据点。

例如:

select s1, top_k(s1, 'k'='2'), bottom_k(s1, 'k'='2') from root.sg1.d2 where time > 2020-12-10T20:36:15.530+08:00;

结果:

+-----------------------------+--------------------+------------------------------+---------------------------------+
|                         Time|      root.sg1.d2.s1|top_k(root.sg1.d2.s1, "k"="2")|bottom_k(root.sg1.d2.s1, "k"="2")|
+-----------------------------+--------------------+------------------------------+---------------------------------+
|2020-12-10T20:36:15.531+08:00| 1531604122307244742|           1531604122307244742|                             null|
|2020-12-10T20:36:15.532+08:00|-7426070874923281101|                          null|                             null|
|2020-12-10T20:36:15.533+08:00|-7162825364312197604|          -7162825364312197604|                             null|
|2020-12-10T20:36:15.534+08:00|-8581625725655917595|                          null|             -8581625725655917595|
|2020-12-10T20:36:15.535+08:00|-7667364751255535391|                          null|             -7667364751255535391|
+-----------------------------+--------------------+------------------------------+---------------------------------+
Total line number = 5
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