Categories:: Aggregate functions (General) , Window functions (General, Window Frame)

AVG¶

Returns the average of non-NULL records. If all records inside a group are NULL, the function returns NULL.

Syntax¶

Aggregate function

AVG( [ DISTINCT ] <expr1> )

Window function

AVG( [ DISTINCT ] <expr1> ) OVER (
                                 [ PARTITION BY <expr2> ]
                                 [ ORDER BY <expr3> [ { ASC | DESC } ] [ NULLS { FIRST | LAST } ] [ <window_frame> ] ]
                                 )

For detailed window_frame syntax, see Window function syntax and usage.

Arguments¶

expr1: This is an expression that evaluates to a numeric data type (INTEGER, FLOAT, DECIMAL, etc.).
expr2: This is the optional expression to partition by.
expr3: This is the optional expression to order by within each partition.

Usage notes¶

When passed a VARCHAR expression, this function implicitly casts the input to floating point values. If the cast cannot be performed, an error is returned.

When this function is called as a window function with an OVER clause that contains an ORDER BY clause:
- A window frame is required. If no window frame is specified explicitly, the following implied window frame is used:
  
  RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
  
  For more information about window frames, including syntax, usage notes, and examples, see Window function syntax and usage.
- Using the keyword DISTINCT inside the window function is prohibited and results in a compile-time error.

Examples¶

Setup:

CREATE OR REPLACE TABLE avg_example(int_col int, d decimal(10,5), s1 varchar(10), s2 varchar(10));
INSERT INTO avg_example VALUES
    (1, 1.1, '1.1','one'), 
    (1, 10, '10','ten'),
    (2, 2.4, '2.4','two'), 
    (2, NULL, NULL, 'NULL'),
    (3, NULL, NULL, 'NULL'),
    (NULL, 9.9, '9.9','nine');

Show the data:

SELECT * 
    FROM avg_example 
    ORDER BY int_col, d;
+---------+----------+------+------+
| INT_COL |        D | S1   | S2   |
|---------+----------+------+------|
|       1 |  1.10000 | 1.1  | one  |
|       1 | 10.00000 | 10   | ten  |
|       2 |  2.40000 | 2.4  | two  |
|       2 |     NULL | NULL | NULL |
|       3 |     NULL | NULL | NULL |
|    NULL |  9.90000 | 9.9  | nine |
+---------+----------+------+------+

Calculate the average of the columns that are numeric or that can be converted to numbers:

SELECT AVG(int_col), AVG(d)
    FROM avg_example;
+--------------+---------------+
| AVG(INT_COL) |        AVG(D) |
|--------------+---------------|
|     1.800000 | 5.85000000000 |
+--------------+---------------+

Combine AVG with GROUP BY to calculate the averages of different groups:

SELECT int_col, AVG(d), AVG(s1) 
    FROM avg_example 
    GROUP BY int_col
    ORDER BY int_col;
+---------+---------------+---------+
| INT_COL |        AVG(D) | AVG(S1) |
|---------+---------------+---------|
|       1 | 5.55000000000 |    5.55 |
|       2 | 2.40000000000 |    2.4  |
|       3 |          NULL |    NULL |
|    NULL | 9.90000000000 |    9.9  |
+---------+---------------+---------+

Use as a simple window function:

SELECT 
       int_col,
       AVG(int_col) OVER(PARTITION BY int_col) 
    FROM avg_example
    ORDER BY int_col;
+---------+-----------------------------------------+
| INT_COL | AVG(INT_COL) OVER(PARTITION BY INT_COL) |
|---------+-----------------------------------------|
|       1 |                                   1.000 |
|       1 |                                   1.000 |
|       2 |                                   2.000 |
|       2 |                                   2.000 |
|       3 |                                   3.000 |
|    NULL |                                    NULL |
+---------+-----------------------------------------+