mysql结合多个联接

Question

I've been struggling with altering my query for days now and I just can't get the result I want. I kind of hoping someone can help me out how to change my query.

Having the following query now:

SELECT 
    t.tId,
    t.tName,
    a.aId,
    a.aName,
    u.uId,
    u.uName
FROM
    tableT t
    LEFT JOIN t_a ta USING (tId)
    LEFT JOIN t_u tu USING (tId)
    LEFT JOIN tableA a ON a.aId = ta.aId
    LEFT JOIN tableU u ON u.uId = tu.uId

It returns rows from tableT with matched row in tableA and tableU. Now I have to change it to get a result where all row from tableA are returned as well.

If I'm not mistaken I want a FULL OUTER JOIN with tableA and a LEFT JOIN with tableU. (I'm aware that FULL OUTER JOIN doesn't exists, which makes it even more confusing for me)

table t_a contains many to many relations and table t_u contains many to one relations from tableT's respective.

In short, when I search for a value, I want to have the following rows to be returned: Any tableT row containing the value and matched rows from tableU and matched rows from tableA. Any other (unmatched) tableA row containing the value. No other (unmatched) rows from tableU.

Values needed before:

tableT   tableA    tableU
ANY      ANY       ANY
ANY      NULL      ANY
ANY      NULL      NULL

Values needed now:

  tableT      tableA        tableU
  ANY          ANY           ANY
  ANY          NULL          ANY
  ANY          NULL          NULL
**NULL**     **ANY**       **NULL**

My apologies when I'm asking for help under the wrong circumstances. Thanks in advance for any help.

A have a fiddle here: http://sqlfiddle.com/#!2/f6301/11

It returns all desired rows except for the row containing:

TID    TNAME    AID    ANAME    UID    UNAME
NULL   NULL     4      aName4   NULL   NULL

Answer 1

I think what you want is to start with all the tid s from tableT and t_a :

FROM ((SELECT t.tID from tableT) UNION
      (SELECT ta.tID from tableA t_a)
     ) ids left outer join
     tableT t
     USING (tId) LEFT JOIN
     t_i ti
     USING (tId) LEFT JOIN
     tableA a
     ON a.aId = ta.aId LEFT JOIN
     tableU u
     ON u.uId = ti.uId

Answer 2

table t_a contains many to many relations and table t_u contains many to one relations from tableT's respective.

But there is no relationship between t_a and t_u. Yet you are trying to get them to share tuple space with each other.

Look at it like this. TableT is a super class. Table t_a extends TableT to form a class of its own. Table t_u also extends TableT to form a class of its own. So, while t_a and t_u both extend TableT, they form separate classes (entities) that are really independent of each other. There is really no way to shoehorn them into one entity expression (tuple).

To put in yet another way, you are trying to mix apples and oranges and a relational database does not do fruit salad very well.

Answer 3

If I'm not mistaken the query I need is as follows:

SELECT
    t.tId,
    t.tName,
    a.aId,
    a.aName,
    u.uId,
    u.uName
FROM
    tableT t
    LEFT JOIN t_a ta USING (tId)
    LEFT JOIN t_u ti USING (tId)
    LEFT JOIN tableA a USING (aId)
    LEFT JOIN tableU u USING (uId)
UNION
SELECT
    t.tId,
    t.tName,
    a.aId,
    a.aName,
    NULL,
    NULL
FROM
    tableT t
    RIGHT JOIN t_a ta USING (tId)
    RIGHT JOIN tableA a USING (aId)
    WHERE t.tId IS NULL

But I'm sure it can be optimized or different.

It will/should now return all rows from tableT with possible related tableA data and possible related tableU data and in addition any other tableA rows.