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# 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()`, `COUNT_IF()` 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| COUNT_IF    | Find the number of data points that continuously meet a given condition and the number of data points that meet the condition (represented by keep) meet the specified threshold. | BOOLEAN                  | `[keep >=/>/=/!=/</<=]threshold`：The specified threshold or threshold condition, it is equivalent to `keep >= threshold` if `threshold` is used alone, type of `threshold` is `INT64`<br/> `ignoreNull`：Optional, default value is `true`；If the value is `true`, null values are ignored, it means that if there is a null value in the middle, the value is ignored without interrupting the continuity. If the value is `true`, null values are not ignored, it means that if there are null values in the middle, continuity will be broken | INT64     |

## COUNT

### example

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

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

## COUNT_IF

### Grammar
```sql
count_if(predicate, [keep >=/>/=/!=/</<=]threshold[, 'ignoreNull'='true/false'])
```
predicate: legal expression with `BOOLEAN` return type

use of threshold and ignoreNull can see above table

>Note: count_if is not supported to use with SlidingWindow in group by time now

### example

#### raw data

``` 
+-----------------------------+-------------+-------------+
|                         Time|root.db.d1.s1|root.db.d1.s2|
+-----------------------------+-------------+-------------+
|1970-01-01T08:00:00.001+08:00|            0|            0|
|1970-01-01T08:00:00.002+08:00|         null|            0|
|1970-01-01T08:00:00.003+08:00|            0|            0|
|1970-01-01T08:00:00.004+08:00|            0|            0|
|1970-01-01T08:00:00.005+08:00|            1|            0|
|1970-01-01T08:00:00.006+08:00|            1|            0|
|1970-01-01T08:00:00.007+08:00|            1|            0|
|1970-01-01T08:00:00.008+08:00|            0|            0|
|1970-01-01T08:00:00.009+08:00|            0|            0|
|1970-01-01T08:00:00.010+08:00|            0|            0|
+-----------------------------+-------------+-------------+
```

#### Not use `ignoreNull` attribute (Ignore Null)

SQL:
```sql
select count_if(s1=0 & s2=0, 3), count_if(s1=1 & s2=0, 3) from root.db.d1
```

Result:
```
+--------------------------------------------------+--------------------------------------------------+
|count_if(root.db.d1.s1 = 0 & root.db.d1.s2 = 0, 3)|count_if(root.db.d1.s1 = 1 & root.db.d1.s2 = 0, 3)|
+--------------------------------------------------+--------------------------------------------------+
|                                                 2|                                                 1|
+--------------------------------------------------+--------------------------------------------------
```

#### Use `ignoreNull` attribute

SQL:
```sql
select count_if(s1=0 & s2=0, 3, 'ignoreNull'='false'), count_if(s1=1 & s2=0, 3, 'ignoreNull'='false') from root.db.d1
```

Result:
```
+------------------------------------------------------------------------+------------------------------------------------------------------------+
|count_if(root.db.d1.s1 = 0 & root.db.d1.s2 = 0, 3, "ignoreNull"="false")|count_if(root.db.d1.s1 = 1 & root.db.d1.s2 = 0, 3, "ignoreNull"="false")|
+------------------------------------------------------------------------+------------------------------------------------------------------------+
|                                                                       1|                                                                       1|
+------------------------------------------------------------------------+------------------------------------------------------------------------+
```