Aggregate functions are functions that take a set of values—a column or an expression including a column name—in a result set and return a single value. For example, we can query a table that contains students' test scores to find the average by using the AVG() function. In SQL, the basic aggregate functions are:
AVG()— Calculates average
COUNT()— Returns the number of rows
MAX()— The highest value in the set of values
MIN()— The smallest value in the set
SUM()— The sum of the values
When we use an aggregate function in a select list, we can't use anything else but aggregate functions in the select list—unless we use a GROUP BY clause.
In the previous chapter, we considered a table of fruit.
Fruit Color ...