无法从MySQL查询中获得所需的结果

Question

I am trying to write a query in MySQL with output in PHP, but it's proving rather difficult.

I have a table with 3 columns (yes I know the database layout for this isn't the best, but I can't change this, the client has other software using this db with this exact layout)

Amount - Product - Package 
2      - Apple   - Fruitbasket1
1      - Pear    - Fruitbasket1
5      - Grape   - Fruitbasket1
2      - Apple   - Fruitbasket2
1      - Pear    - Fruitbasket2
9      - Banana  - Fruitbasket2

So far I came up with this:

SELECT package 
FROM `data` 
WHERE package IN 
(
  SELECT package 
  FROM `data` 
  WHERE product = 'apple' AND amount = '2'
) 
AND package IN 
(
  SELECT package 
  FROM `data` 
  WHERE product = 'pear' AND amount ='1'
) 
AND package IN 
(
  SELECT package 
  FROM `data` 
  WHERE product = 'grape' AND amount = '5'
) 
LIMIT 0,1

The issue is that when the customer would fill out "apple" and "2" on the form, it would return all the baskets containing 2 apples. What I need is a statement that will only accept the exact products and their amounts to return the one basket those ingredients belong to, or nothing at all.

So even though 1 pear and 2 apples are in Fruitbasket1, it should not give Fruitbasket1 as a result if the other part, namely 5 grapes, are not specified by the customer.

Answer 1

this query will return all packages where the only product is 2 Apples

select package from `data`
group by package
having count(case when amount = 2 and product = 'Apple' then 1 end) = 1
and count(*) = 1

if you want 1 pear and 2 apples for example

select package from `data`
group by package
having count(
  case 
    when (amount = 2 and product = 'Apple') or (amount = 1 and product = 'Pear') 
    then 1 
  end) = 2
and count(*) = 2

you could also write this as

select package from `data`
group by package
having count(case when amount = 2 and product = 'Apple' then 1 end) = 1
   and count(case when amount = 1 and product = 'Pear' then 1 end) = 1
   and count(*) = 2

Answer 2

I only have Oracle handy so you may have to adjust the syntax somewhat, but following your original style I've added a "not in" section to make sure the basket contains only the fruits you are looking for. Here are some inserts with a couple of examples:

create table data (amount integer, product varchar(12), package varchar(16));

insert into data values (2, 'Apple', 'Fruitbasket1');
insert into data values (1, 'Pear', 'Fruitbasket1');
insert into data values (5, 'Grape', 'Fruitbasket1');
insert into data values (2, 'Apple', 'Fruitbasket2');
insert into data values (1, 'Pear', 'Fruitbasket2');
insert into data values (9, 'Banana', 'Fruitbasket2');
insert into data values (2, 'Apple', 'Fruitbasket3');
insert into data values (2, 'Apple', 'Fruitbasket4');
insert into data values (1, 'Pear', 'Fruitbasket4');


SELECT package 
FROM data 
WHERE package IN 
(
  SELECT package 
  from data 
  WHERE product = 'Apple' AND amount = '2'
)
and package not in
(
  SELECT package 
  from data 
  WHERE product <> 'Apple'
)
group by package
;


SELECT package 
FROM data 
WHERE package IN 
(
  SELECT package 
  from data 
  WHERE product = 'Apple' AND amount = '2'
) 
AND package IN 
(
  SELECT package 
  FROM data 
  WHERE product = 'Pear' AND amount ='1'
) 
and package not in
(
  SELECT package 
  from data 
  WHERE product <> 'Apple' and product <> 'Pear'
)
group by package
;