# Aggregate Functions

* sum(expression)
    
    Description: Specifies the sum of expressions across all input values.
    
    Return type:
    
    Generally, it is the same as the argument data type. In the following cases, type conversion occurs:
    
    * **BIGINT** for **SMALLINT** or **INT** arguments
        
    * **NUMBER** for **BIGINT** arguments
        
    * **DOUBLE PRECISION** for floating-point arguments
        
    
    Example:
    
    ```plaintext
    ""openGauss=# SELECT SUM(amount) FROM customer_t1;
      sum
    -------
     14200
    (1 row)
    ```
    
* max(expression)
    
    Description: Specifies the maximum value of expressions across all input values.
    
    Parameter type: any array, numeric, string, date/time type, or IPv4 and IPv6 addresses (INET and CIDR data types)
    
    Return type: same as the argument data type
    
    Example:
    
    ```plaintext
    ""openGauss=# SELECT MAX (c_customer_sk) FROM customer_t1;
     max
    ------
     9976
    (1 row)
    ```
    
* min(expression)
    
    Description: Specifies the minimum value of expressions across all input values.
    
    Parameter type: any array, numeric, string, date/time type, or IPv4 and IPv6 addresses (INET and CIDR data types)
    
    Return type: same as the argument data type
    
    Example:
    
    ```plaintext
    ""openGauss=#  SELECT MIN (c_customer_sk) FROM customer_t1;
    min
    ------
     3869
    (1 row)
    ```
    
* avg(expression)
    
    Description: Specifies the average (arithmetic mean) of all input values.
    
    Return type:
    
    **NUMBER** for any integer-type argument.
    
    **DOUBLE PRECISION** for floating-point arguments.
    
    Otherwise, it is the same as the argument data type.
    
    Example:
    
    ```plaintext
    ""openGauss=# SELECT AVG(AMOUNT) FROM customer_t1;
              avg
    -----------------------
     2366.6666666666666667
    (1 row)
    ```
    
* count(expression)
    
    Description: Specifies the number of input rows for which the value of the expression is **NULL**.
    
    Return type: BIGINT
    
    Example:
    
    ```plaintext
    ""openGauss=# SELECT COUNT(c_customer_id) FROM customer_t1;
     count
    -------
         7
    (1 row)
    ```
    
* count(\*)
    
    Description: Returns the number of input rows.
    
    Return type: BIGINT
    
    Example:
    
    ```plaintext
    ""openGauss=# SELECT COUNT(*) FROM customer_t1;
    count
    -------
         8
    (1 row)
    ```
    
* delta
    
    Description: Returns the difference between the current row and the previous row.
    
    Parameter: numeric
    
    Return type: numeric
    
* mode() within group (order by value anyelement)
    
    Description: Returns the value with the highest occurrence frequency in a column. If multiple values have the same frequency, the smallest value is returned. The sorting mode is the same as the default sorting mode of the column type. **value** is an input parameter and can be of any type.
    
    Return type: same as the argument data type
    
    Example:
    
    ```plaintext
    ""openGauss=# select mode() within group (order by value) from (values(1, 'a'), (2, 'b'), (2, 'c')) v(value, tag);
     mode
    ------
        2
    (1 row)
    openGauss=# select mode() within group (order by tag) from (values(1, 'a'), (2, 'b'), (2, 'c')) v(value, tag);
     mode
    ------
     a
    (1 row)
    ```
    

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