MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide

12.19.1 Aggregate Function Descriptions

This section describes aggregate functions that operate on sets of values. They are often used with a GROUP BY clause to group values into subsets.

Table 12.23 Aggregate Functions

Name Description
AVG() Return the average value of the argument
BIT_AND() Return bitwise AND
BIT_OR() Return bitwise OR
BIT_XOR() Return bitwise XOR
COUNT() Return a count of the number of rows returned
COUNT(DISTINCT) Return the count of a number of different values
GROUP_CONCAT() Return a concatenated string
MAX() Return the maximum value
MIN() Return the minimum value
STD() Return the population standard deviation
STDDEV() Return the population standard deviation
STDDEV_POP() Return the population standard deviation
STDDEV_SAMP() Return the sample standard deviation
SUM() Return the sum
VAR_POP() Return the population standard variance
VAR_SAMP() Return the sample variance
VARIANCE() Return the population standard variance

Unless otherwise stated, aggregate functions ignore NULL values.

If you use an aggregate function in a statement containing no GROUP BY clause, it is equivalent to grouping on all rows. For more information, see Section 12.19.3, “MySQL Handling of GROUP BY”.

For numeric arguments, the variance and standard deviation functions return a DOUBLE value. The SUM() and AVG() functions return a DECIMAL value for exact-value arguments (integer or DECIMAL), and a DOUBLE value for approximate-value arguments (FLOAT or DOUBLE).

The SUM() and AVG() aggregate functions do not work with temporal values. (They convert the values to numbers, losing everything after the first nonnumeric character.) To work around this problem, convert to numeric units, perform the aggregate operation, and convert back to a temporal value. Examples:

SELECT FROM_DAYS(SUM(TO_DAYS(date_col))) FROM tbl_name;

Functions such as SUM() or AVG() that expect a numeric argument cast the argument to a number if necessary. For SET or ENUM values, the cast operation causes the underlying numeric value to be used.

The BIT_AND(), BIT_OR(), and BIT_XOR() aggregate functions perform bit operations. They require BIGINT (64-bit integer) arguments and return BIGINT values. Arguments of other types are converted to BIGINT and truncation might occur.