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:
```
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:
```
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:
```
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:
```
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:
```
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:
```
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:
```
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)
```