SQL INNER Join没有给出结果

Question

I have two tables with info as follows:

Table: menu_dishes
dish_id   dish_title     ingredients
DSH01     Bacon & Eggs   Bacon, eggs

Table: menu_dishes_status
dish_id  valid_from  valid_to     price
DSH01    2013-10-10  2013-12-31   10.00
DSH01    2014-01-01  2014-02-28   12.00

The first table contains the dishes, the second, contains the dishes' status. So a dish's current status is one where CURRENT_DATE is between valid_from and valid_to dates, and a retired dish is one where the MAX(valid_to) < CURRENT_DATE.

I am joining these tables and categorizing the data:

'n' NEW => WHERE CURRENT_DATE BETWEEN valid_from AND (valid_from + 1 MOTNH)
'c' CURRENT => WHERE CURRENT_DATE > (valid_from + 1 MOTNH)
'r' RETIRED => the rest of the rows, so the "dish_id" items not in the tables above, BUT 
           returning the values from the row containing MAX(valid_to) date.

The query (with help from the forum) is:

SELECT
    menu_dishes.dish_id,
    menu_dishes.dish_title,
    menu_dishes.ingredients,
    menu_dishes_status.price,
CASE 
    WHEN
        CURRENT_DATE BETWEEN menu_table_status.valid_from 
                         AND DATE_ADD(menu_table_status.valid_from, INTERVAL 1 MONTH) 
        AND CURRENT_DATE < menu_table_status.valid_to
    THEN 'n' 
    WHEN
      CURRENT_DATE > DATE_ADD(menu_table_status.valid_from_date, INTERVAL 1 MONTH) 
      AND CURRENT_DATE < menu_table_status.valid_to
    THEN 'c'
    ELSE 'r'
END as status
FROM menu_dishes
INNER JOIN 
    menu_dishes_status ON (menu_dishes.dish_id = menu_dishes_status.dish_id)
ORDER BY menu_dishes.dish_title ASC

The above returns (in the case of DSH01 data example) two rows, one with $10, and one with $12. I need the 'r' items to contain the price from the most recent time period, or MAX(valid_to)

How do I add this join / condition? I have tried a subquery without success.

Thanks in advance!

Answer 1

You will need to have group the data by menu_dishes_status.dish_id. Max(valid_to) would then work nicely

Try this

FROM menu_dishes
INNER JOIN 
    menu_dishes_status ON (menu_dishes.dish_id = menu_dishes_status.dish_id)
group by menu_dishes_status.dish_id having MAX(valid_to)
ORDER BY menu_dishes.dish_title ASC

Let me know if this works

Answer 2

Try this, it might help.

CASE 

WHEN ((CURRENT_DATE BETWEEN menu_table_status.valid_from AND
      DATE_ADD(menu_table_status.valid_from, INTERVAL 1 MONTH))
      AND CURRENT_DATE < menu_table_status.valid_to)
THEN 'n' 

WHEN  ((CURRENT_DATE > DATE_ADD(menu_table_status.valid_from_date, INTERVAL 1 MONTH))
      AND CURRENT_DATE < menu_table_status.valid_to)
THEN 'c'

ELSE 'r'

END as status

Answer 3

Try it like this, not tested, just off the top of my head, try creating an sql fiddle for more help

SELECT
    menu_dishes.dish_id,
    menu_dishes.dish_title,
    menu_dishes.ingredients,
    menu_dishes_status.price,
CASE 
    WHEN
        CURRENT_DATE BETWEEN menu_table_status.valid_from 
                         AND DATE_ADD(menu_table_status.valid_from, INTERVAL 1 MONTH) 
        AND CURRENT_DATE < menu_table_status.valid_to
    THEN 'n' 
    WHEN
      CURRENT_DATE > DATE_ADD(menu_table_status.valid_from_date, INTERVAL 1 MONTH) 
      AND CURRENT_DATE < menu_table_status.valid_to
    THEN 'c'
    ELSE 'r'
END as status
FROM menu_dishes
INNER JOIN 
menu_dishes_status ON (menu_dishes.dish_id = menu_dishes_status.dish_id)
WHERE menu_dishes_status.valid_to=(SELECT MAX(valid_to) FROM menu_dishes_status WHERE menu_dishes_status.dish_id=menu_dishes.dish_id)
ORDER BY menu_dishes.dish_title ASC

Answer 4

Here's the right SQL. Thank you all for your help:

SELECT
    menu_dishes.dish_id,
    menu_dishes.dish_title,
    menu_dishes.ingredients,
    menu_dishes_status.price,
CASE 
    WHEN
        CURRENT_DATE BETWEEN menu_table_status.valid_from 
                         AND DATE_ADD(menu_table_status.valid_from, INTERVAL 1 MONTH) 
        AND CURRENT_DATE <= menu_table_status.valid_to
    THEN 'n' 
    WHEN
      CURRENT_DATE > DATE_ADD(menu_table_status.valid_from_date, INTERVAL 1 MONTH) 
      AND CURRENT_DATE <= menu_table_status.valid_to
    THEN 'c'
    ELSE 'r'
END as status
FROM menu_dishes
INNER JOIN 
    menu_dishes_status ON (menu_dishes.dish_id = menu_dishes_status.dish_id)
WHERE menu_dishes_status.valid_to_date = (SELECT MAX(intab.valid_to_date)
                                          FROM menu_dishes_status AS intab
                                          WHERE intab.dish_id = menu_dishes_status.dish_id)
ORDER BY menu_dishes.dish_title ASC