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.
- The DISTINCT keyword cannot be used.

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 |
+---------+-----------------------------------------+