SQL aggregate functions return a single value, calculated from values in a column.

Useful aggregate functions:

AVG() - Returns the average value
SELECT AVG(column_name) FROM table_name;
COUNT() - Returns the number of rows
SELECT COUNT(column_name) FROM table_name;
SELECT COUNT(DISTINCT column_name) FROM table_name;
FIRST() - Returns the first value
MYSQL: SELECT column_name FROM table_name
ORDER BY column_name ASC LIMIT 1;
ORACLE: SELECT column_name FROM table_name
WHERE ROWNUM <=1 ORDER BY column_name ASC;
SQLSERVER: SELECT TOP 1 column_name FROM table_name
ORDER BY column_name ASC;
LAST() - Returns the last value
mesma sintaxe que FIRST(), mas usando DESC
MAX() - Returns the largest value
SELECT MAX(column_name) FROM table_name;
MIN() - Returns the smallest value
SELECT MIN(column_name) FROM table_name;
SUM() - Returns the sum
SELECT SUM(column_name) FROM table_name;
GROUP BY - Used with aggregate functions
SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;
HAVING - Filter used with aggregate functions
SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value;

	Creado por dgmagno hace más de 8 años

SQL Aggregate and Scalar Functions