具有表结构的SQL查询

Question

I have a database table structure as follow:

datatype
data
mytable

now datatype has primary key datatypeid, data table has datatypeid as foriegn key and has mytable id as foreign key.

In datatype I have a column called description which has address1, address2 etc

And the values for these addresses are stored in data table using the datatypeid as reference.

So I want to make a select statement to show the ids from mytable and address1, address2 etc as columns, with the values coming from data.values as follow:

id address1  address2
1  test add  test add2
2  test add  test add2
2  test add  test add2

here is my query so far but it outputs it in different format:

SELECT     id
FROM       datatype 
INNER JOIN data ON datatype.DataTypeID = data.DataTypeID 
INNER JOIN mytable ON data.ID = mytable.ID

EDIT :
table structure:

datatype 
  -datatypeid int
  -description varchar(50)
data
  -id int
  -datatypeid int
  -datavalue varchar(50)
  -mytableid int
mytable
  -mytableid int
  -datecreated datetime

Sample Data

datatype :
datatypeid  description
1           address1
2           address2

data :
id datatypeid datavalue        mytableid
1   1         george street     1

mytable:
mytableid datecreated
1         2012-02-17 10:06:02.507

Can you help please?

Answer 1

spitballing this, but give it a try

SELECT m.mytableid, CASE WHEN dt.datatypeid = 1 AND d.datatypeid =1 THEN d.datavalue ELSE null END AS "address1"
    , CASE WHEN dt.datatypeid = 2 AND d.datatypeid =2 THEN d.datavalue ELSE null END AS "address2"
    ,m.datecreated    
FROM datatype dt inner join
    data d on dt.datatypeid = d.datatypeid inner join
    mytable m on d.mytableid = m.mytableid

Answer 2

I don't think that this structure is optimal for what you want, but if you are stuck with it....

something like this might help.(i have not tested it at all)

My assumptions

• there is some sort of predicate...just not listed
• not every id has 2 addresses, therefore they would be eliminated if you did an inner join
• the mytable serves some purpose, i just don't see why it is here from the example.

• datatype table has more values than address1 and address2

   WITH address1 as ( SELECT id,datavalue FROM data WHERE datatypeid = <datatypeid for addr1> ), address2 as( SELECT id,datavalue FROM data WHERE datatypeid = <datatypeid for addr2> ) SELECT d.id, a1.datavalue as address1, a2.datavalue as address2 FROM data d LEFT OUTER JOIN address1 a1 ON d.id = a1.id LEFT OUTER JOIN address2 a2 ON d.id = a2.id 

again, you might will have to do some tweaking to the sql, because it would not perform in a production environment with a lot of rows

Answer 3

Don't understand well what's the structure of your database but I can help with my suggestion:

SELECT     B.id
FROM       datatype A INNER JOIN
                      data B ON datatype.DataTypeID = data.DataTypeID INNER JOIN
                      mytable C ON data.ID = mytable.ID

This helps to be sure that there's no conflict between attributes.

RQ: You have put data.ID with ID (uppercase) in INNER JOIN and in SELECT you have put in lowercase. This may cause the problem, I'm not sure.