Question

So, I have three tables, table “local”, table item and table “item_local”. Here is data contains in the tables:

Table "local"
    ID  Local
    1   Ru
    2   En

Table "item"
    ID  Name
    1   Test1
    2   Test2
    3   Test3

Table "item_local"  
    ID  ItemID  LocalID Text
    1   1       1       Test-Ru
    2   1       2       Test-En
    3   2       1       Test-Ru
    4   2       2       Test-En
    5   3       1       Test-Ru

My problem is I don’t know the SELECT query with local that will display the result such as below:

Result if i select with local "Ru":
    ID  ItemID  LocalID Text
    1   1       1       Test-Ru 
    3   2       1       Test-Ru 
    5   3       1       Test-Ru

Result if i select with local "En": 
    ID  ItemID  LocalID Text
    2   1       2       Test-En
    4   2       2       Test-En
    5   3       1       Test-Ru

Is there a query or any other way to get such the result?

Anyway, thanks for helping.

Answer 1

SELECT il.ID, il.ItemID, il.LocalID, il.Text
FROM item i
JOIN local l ON l.Local='Ru'
[LEFT] JOIN item_local il ON i.ID=il.ItemID AND il.LocalID=l.ID

Note that the table item is not necessary. However, I guess you would like to see the missing entries in the step. This can be done by using the LEFT JOIN and add the condition WHERE il.ID IS NULL.

Edit: Oh, is missed the fallback to “Ru”.

-- try 'En'
SELECT il.ID, il.ItemID, il.LocalID, il.Text
FROM item_local il
JOIN local l ON l.Local='En' AND l.ID=il.LocalID
UNION
-- fallback to 'Ru'
SELECT il.ID, il.ItemID, il.LocalID, il.Text
FROM item_local il
JOIN local l ON l.Local='Ru' AND l.ID=il.LocalID
WHERE il.ItemID NOT IN (
    SELECT il.ItemID
    FROM item_local il
    JOIN local l ON l.Local='En' AND l.ID=il.LocalID
)