docs/zh/UserGuide/UDF-Library/M4.md

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## M4

### M4

#### 函数简介

本函数使用 MAC (merging all chunks) 方法执行M4聚合查询。

**函数名：** M4

**输入序列：** 仅支持单个输入序列，类型为 INT32 / INT64 / FLOAT / DOUBLE。

**参数：**

+ `tqs`: 查询的开始时间（含）。
+ `tqe`: 查询的结束时间（不含）。
+ `w`: M4聚合中的时间跨度数量。

**输出序列：** 每个时间跨度的首、尾、最小和最大值。

`[tqs+(tqe-tqs)/w*(i-1),tqs+(tqe-tqs)/w*i), i=1,...,w.`

**说明：**
+ 函数当前仅适用于 `research/M4-visualization` 分支。
+ 输入参数需确保 `(tqe-tqs)` 是 `w` 的倍数。
+ 查询时需在 where 语句后添加 `time>=tqs and time<tqe`。

#### 使用示例

输入序列:

```
+-----------------------------+------------------+
|                         Time|root.vehicle.d0.s0|
+-----------------------------+------------------+
|1970-01-01T08:00:00.001+08:00|               5.0|
|1970-01-01T08:00:00.002+08:00|              15.0|
|1970-01-01T08:00:00.005+08:00|              10.0|
|1970-01-01T08:00:00.008+08:00|               8.0|
|1970-01-01T08:00:00.010+08:00|              20.0|
|1970-01-01T08:00:00.020+08:00|              20.0|
|1970-01-01T08:00:00.025+08:00|               8.0|
|1970-01-01T08:00:00.027+08:00|              20.0|
|1970-01-01T08:00:00.030+08:00|              40.0|
|1970-01-01T08:00:00.033+08:00|               9.0|
|1970-01-01T08:00:00.035+08:00|              10.0|
|1970-01-01T08:00:00.040+08:00|              20.0|
|1970-01-01T08:00:00.045+08:00|              30.0|
|1970-01-01T08:00:00.052+08:00|               8.0|
|1970-01-01T08:00:00.054+08:00|              18.0|
|1970-01-01T08:00:00.120+08:00|               8.0|
+-----------------------------+------------------+
```

用于查询的 SQL 语句:

```sql
select M4(s0,'tqs'='0','tqe'='100','w'='4') from root.vehicle.d0 where time>=0 and time<100
```

输出序列:

```
+-----------------------------+----------------------------------------------------------------------------------+
|                         Time|                           M4(root.vehicle.d0.s0, "tqs"="0", "tqe"="100", "w"="4")|
+-----------------------------+----------------------------------------------------------------------------------+
|1970-01-01T08:00:00.000+08:00|  FirstPoint=(1,5.0), LastPoint=(20,20.0), BottomPoint=(1,5.0), TopPoint=(10,20.0)|
|1970-01-01T08:00:00.025+08:00|FirstPoint=(25,8.0), LastPoint=(45,30.0), BottomPoint=(25,8.0), TopPoint=(30,40.0)|
|1970-01-01T08:00:00.050+08:00|FirstPoint=(52,8.0), LastPoint=(54,18.0), BottomPoint=(52,8.0), TopPoint=(54,18.0)|
|1970-01-01T08:00:00.075+08:00|                                                                             empty|
+-----------------------------+----------------------------------------------------------------------------------+
```