The result of a query can be the result of one or more aggregate functions. Aggregate functions return a single value from a set of rows. An aggregate can be used with a column name (for example, AVG(salary)) or in combination with a more complex column expression (for example, AVG(salary * 1.07)). The column expression can be preceded by the DISTINCT operator. The DISTINCT operator eliminates duplicate values from an aggregate expression.
Table 16. Aggregate Functions The average of the values in a numeric column expression. For example, AVG(salary) returns the average of all salary column values. The number of values in any column expression. For example, COUNT(name) returns the number of name values. When using COUNT with a column name, COUNT returns the number of non-NULL column values. A special example is COUNT(*), which returns the number of rows in the set, including rows with NULL values. The maximum value in any column expression. For example, MAX(salary) returns the maximum salary column value. The minimum value in any column expression. For example, MIN(salary) returns the minimum salary column value. The total of the values in a numeric column expression. For example, SUM(salary) returns the sum of all salary column values.Except for COUNT(*), all aggregate functions exclude NULL values. The returned value type for COUNT is INTEGER and for MIN, MAX, and AVG it is the same type as the column.
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