两个字段的总和

Question

I have a mysql table with 2 fields: numPears (int) and numApples (int) and i'd like to have a numFruit (int) that automatically get these 2 values and sum them. Is that possible?

Example

So that if a query

INSERT INTO strange_table (fruitID, numPears, numApples) VALUES (1, 1, 5);

And then query

SELECT numFruit FROM strange_table WHERE fruitID = 1;

It returns me 6 .

Answer 1

If you are looking to create a static value every time a new row comes into the DB, use a trigger. See http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html and in particular, triggers on insert and update.

-- You've clarified your question! I think stored procedures are more what you are looking for now!

http://dev.mysql.com/doc/refman/5.0/en/create-procedure.html

This lets you create a function inside MySQL called numFruit which returns the sum of the other two columns.

Answer 2

SELECT (numPears + numApples) AS numFruit FROM strange_table WHERE fruitID = 1;

Answer 3

If you are using PHP

$pears = 5;
$apples= 1;

$query = "INSERT INTO strange_table (fruitID, numPears, numApples, numFruit) VALUES (1, $pears, $apples, " . ($pears + $apples) . ")";

Answer 4

你所谈论的是一个“计算列”它看起来不像MySql目前支持那些。