Oracle SQL连接三个表

Question

I have three Tables and I wanted the join query or relevant for the below mentioned results

 Types ( Table One)
 -------
 typeId
 -------
 square
 circle
 triangle


 Sets ( Table Two)
 ------
 id setValue setName
 ------------------
 1    one      setOne
 2    two      setTwo
 3    three    setThree


 Formation ( Table Three ) Types and sets are foreign keys to the other tables
 ---------
 id setValue  types     extra   notes
 --------------------------------------
 1     two     circle     5       xyz
 2     three   square     4       abc

I want to join this table and get result in such way , always i should get all the types displayed for the input gives as

if User choose set value as 'two' then result should be

 types      setValue        extra       notes
 --------------------------------------------
 square     null            null        null
 circle     two             5           xyz
 triangle   null            null        null

if user choose type value as 'square' then the result should be

  types     setValue        extra       notes
 --------------------------------------------
 square     three           4           abc
 circle     null            null        null
 triangle   null            null        null

if suppose user choose set value as 'rectangle' then the result should be

 types      setValue        extra       notes
--------------------------------------------
 square     null            null        null
 circle     null            null        null
 triangle   null            null        null

Looking forward for solution oracle 10g compatible code

Answer 1

SELECT F.types, F.setValue, F.extra, F.notes
FROM types t
LEFT JOIN Formation F
 on t.typeID = F.Types
 AND ((F.SetValue = 'YourSetInput')
  OR (F.Types = 'YourTypesInput'))

By using a left outer join we always keep all the types. By putting limiting criteria on the join and not in a where clause we don't have to worry about accidently excluding the null values you want to see.

This however does have one draw back in that if both setvalue and types are keyed in both would return. This may or may not be the desired result as the use case hasn't been covered.

So in recap

Return all the tables every time regardless of any other criteria.
Then return the criteria from formation that matches the selected inputs for type or set.