How to use avg function?

问题

I'm new at php and mysql stuff and i'm trying to use an avg function but i don't know how to.

I'm trying to do something like this:

mysql_connect(localhost,$username,$password);

@mysql_select_db($database) or die ("Did not connect to $database");

mysql_query("AVG(column1) FROM table1 ") or die(mysql_error());

mysql_close();

echo AVG(column1);

(Q1)I'd like to see the value printed in the screen, but i'm getting nothing but an error message. How could I print this average on the screen ?

(Q2)If I had a column month in my table1, how could I print the averages by the months ?

Sorry for any bad English, and thanks for the attention.

回答1:

Solution for Q1: SELECT AVG(column1) FROM table1

Solution for Q2: SELECT AVG(column1), month FROM table1 GROUP BY month

回答2:

What to read?

MySQL SELECT syntax
MySQL AVG() function - there is even an example of exactly what you need
PHP mysql_fetch_assoc() function which is one of several ways to retrieve data from result set
btw: PDO is much better for database communication in PHP

Ad. 1:

$sql    = 'SELECT AVG(col_name_1) AS avgColName FROM tbl_name;';
$query  = mysql_query($sql);
$result = mysql_fetch_assoc($query);

var_dump($result['avgColName']);

Ad. 2:

SELECT ... FROM ... GROUP BY MONTH(date_col_name);

回答3:

You need to return the result of the query into a variable which you can then use.

For example:

$query = "AVG(column1) FROM table1";     
$result = mysql_query($query);

// Print out result
while($row = mysql_fetch_array($result)) {
echo $row['AVG(column1)'];
}

来源：https://stackoverflow.com/questions/3010715/how-to-use-avg-function

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php

sql

mysql

average