# Aggregate Functions

About 1 min

# Aggregate Functions

Aggregate functions are many-to-one functions. They perform aggregate calculations on a set of values, resulting in a single aggregated result.

All aggregate functions except `COUNT()`

ignore null values and return null when there are no input rows or all values are null. For example, `SUM()`

returns null instead of zero, and `AVG()`

does not include null values in the count.

The aggregate functions supported by IoTDB are as follows:

Function Name | Function Description | Allowed Input Data Types | Output Data Types |
---|---|---|---|

SUM | Summation. | INT32 INT64 FLOAT DOUBLE | DOUBLE |

COUNT | Counts the number of data points. | All types | INT |

AVG | Average. | INT32 INT64 FLOAT DOUBLE | DOUBLE |

EXTREME | Finds the value with the largest absolute value. Returns a positive value if the maximum absolute value of positive and negative values is equal. | INT32 INT64 FLOAT DOUBLE | Consistent with the input data type |

MAX_VALUE | Find the maximum value. | INT32 INT64 FLOAT DOUBLE | Consistent with the input data type |

MIN_VALUE | Find the minimum value. | INT32 INT64 FLOAT DOUBLE | Consistent with the input data type |

FIRST_VALUE | Find the value with the smallest timestamp. | All data types | Consistent with input data type |

LAST_VALUE | Find the value with the largest timestamp. | All data types | Consistent with input data type |

MAX_TIME | Find the maximum timestamp. | All data Types | Timestamp |

MIN_TIME | Find the minimum timestamp. | All data Types | Timestamp |

**Example:** Count Points

```
select count(status) from root.ln.wf01.wt01;
```

Result:

```
+-------------------------------+
|count(root.ln.wf01.wt01.status)|
+-------------------------------+
| 10080|
+-------------------------------+
Total line number = 1
It costs 0.016s
```