复杂的SELECT MySQL陈述式

Question

I have run into an issue selecting data from my MySQL database.

For example, I have a table with the following columns & tables:

Table name: farming

id | animal | amount | food
----------------------------
1  |   Cow  |    10  | Grass
12 |  Sheep |    19  | Grass
23 |  Lion  |     1  | Everything
29 |  Lamb  |     3  | Grass
102|   Pig  |     8  | Everything
...

I want to get the amount from all the rows that match the food type of a selected id .

Eg If I choose id: 102 then it would get the amount from ALL rows where the food = 'Everything'

SELECT amount FROM farming WHERE food = '".$_GET['food']."' **IS THE SAME TYPE AS IT IS IN** id = '1'"; // This should select 10 , 19 and 3 from amount (as id = 1 's foodtype is Grass , so it should select amount from all rows where foodtype = grass.

** is where I'm facing issues, I've tried various statements and can't seem to get it to work.

Answer 1

You could use group by clause which will sum up all value from amount column whre food = 'Grass'

SELECT SUM(amount) ammount FROM farming 
      WHERE food = (select food FROM farming where id = 102) 
      GROUP BY food

Answer 2

This should do the trick

select  amount
from    farming
where   food = (
            select  food
            from    farming
            where   id = 1
        )