DataBase -- FUNCTION

SELECT function(列) FROM 表

SELECT AVG(column_name) FROM table_name

COUNT(column_name)返回指定列的值得数目（NULL不计入）
SELECT COUNT(column_name) FROM table_name

COUNT(*)返回表中的记录数目
SELECT COUNT(*) FROM table_name

COUNT(DISTINCT column_name)返回指定列的不同值的数目
SELECT COUNT(DISTINCT column_name) FROM table_name

SELECT FIRST(column_name) FROM table_name
(可以先用ORDER BY对记录排序)

SELECT LAST(column_name) FROM table_name

SELECT MAX/MIN(column_name) FROM table_name

SELECT SUM(column_name) FROM table_name

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name

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

SELECT UCASE/LCASE(column_name) FROM table_name

SELECT MID(column_name, start[,length]) FROM table_name
其中，start规定开始位置（起始值是1）
     length要返回的字符数。如果省略，则MID()函数返回剩余文本。

SELECT LEN(column_name) FROM table_name

SELECT ROUND(column_name, decimals) FROM table_name

SELECT NOW() FROM table_name

SELECT FORMAT(column_name, formate) FROM table_name