Self join with inner and outer join query - sql

Question

I have a table that is set up so that one column (attribute) contains information like first name, last name, account number and any other information related to a thing in the database. Another column (attributeType) contains a number indicating what the attribute is e.g. 1 might be first name, 2 last name and 3 account number etc. There is another column (enddate) indicating if the record is current by having a date there. Usually it will be set to the year 9999 when current and some date in the past otherwise. All data describing the same thing has a unique value too in another column (entity) so that each record with the same number in the entity column will be describing the one person. E.g.
entity attribute attributetype enddate
------ --------- ------------- --------
1 ben 1 9999-1-1
1 alt 2 9999-1-1
1 12345 3 9999-1-1
2 sam 1 9999-1-1
2 smith 2 9999-1-1
2 98765 3 1981-1-1
I want to select a person from the above table with a specific 1st and last name where the name will be current but not output the account number if it is not. Assuming the table is called tblAccount I do the following for the name part:
select ta1.attribute '1st Name', ta2.attribute 'last name'
from tblAccount ta1
inner join tblAccount ta2 on ta1.entity = ta2.entity
where ta1.attribute = 'sam' and ta2.attribute = 'smith'
and ta1.attributetype = 1 and ta2. attributetype = 2
and ta1.enddate > getdate() and ta2.enddate > getdate()
and it outputs the first and last names as expected, but when I want to include the account number column I get nothing output:
select ta1.attribute '1st Name', ta2.attribute 'last name', ta3.attribute 'account#'
from tblAccount ta1
inner join tblAccount ta2 on ta1.entity = ta2.entity
left join tblAccount ta3 on ta1.entity = ta3.entity
where ta1.attribute = 'sam' and ta2.attribute = 'smith'
and ta1.attributetype = 1 and ta2. attributetype = 2
and ta1.enddate > getdate() and ta2.enddate > getdate()
and ta3.attributetype = 3 and ta3.enddate > getdate()
What I would like to see is the first and last names output with nothing in the account# column in the above case where it is not current. What am I doing wrong and how can I correct this query?

Answer 1

You have to move the date comparison to the join condition:
select ta1.attribute '1st Name'
, ta2.attribute 'last name'
, ta3.attribute 'account#'
from tblAccount ta1
inner join tblAccount ta2
on ta1.entity = ta2.entity
and ta1.attributetype = 1 and ta2. attributetype = 2
and ta1.enddate > getdate() and ta2.enddate > getdate()
left join tblAccount ta3 on ta1.entity = ta3.entity
and ta3.attributetype = 3 and ta3.enddate > getdate()
where ta1.attribute = 'sam' and ta2.attribute = 'smith'
When it's in the where clause it's comparing getdate() to NULL if there is no account, which returns NULL. So no record.
EDIT:
In response to the valid concern about multiple valid records, and to make the code a little more maintenance freindly:
DECLARE #FNAME VARCHAR(50) = 'sam'
, #LNAME VARCHAR(50) = 'smith'
, #now DATETIME2(7) = GETDATE();
SELECT
name.[1st Name]
, name.[last name]
, name.entity
,
(
select
top 1
ta3.attribute
FROM tblAccount ta3
WHERE
ta3.entity = name.entity
and
ta3.attributetype = 3
and
ta3.enddate > #now
ORDER BY
ta3.enddate
)
FROM
(
select
ta1.attribute '1st Name'
, ta2.attribute 'last name'
, ta.entity
, ROW_NUMBER()
OVER(
PARTITION BY
ta1.entity
ORDER BY
ta1.enddate
) r
from
tblAccount ta1
inner join tblAccount ta2
on
ta1.entity = ta2.entity
and
ta2. attributetype = 2
and
ta2.enddate > #now
and
ta2.attribute = #LNAME
where
ta1.attributetype = 1
and
ta1.attribute = #fname
and
ta1.enddate > #now
) name
WHERE
NAME.r = 1
;
This code works around the implied assumptions of one entity per first/last name and exactly one enddate after the execution time. The variables are a little more stored proc friendly, and allow you to change the "as of" date. And if you're stuck with EAV, you will likely want stored procs. I'm taking the first record ending after the date in question, on the assumption that any later record(s) should only be valid after that one expires. Maybe it's overkill, since it's beyond the scope of the OP's question but it's a valid point.
I say "stuck with EAV". While EAV isn't always bad; neither is shooting someone in the back. In either case, you'd better have solid justification if you expect to get it past a jury. In a NoSQL storage pattern it's fine, but EAV is usually a poor implementation pattern for the RDBMS paradigm.
Though from the OP's later comment, it looks like he's hit on one of the better reasons.

Answer 2

Each attribute is actually a distinct entity in this model, but they are all sharing the same storage in the same physical table (Why?). This yields:
with data as (
select entity = 1, attribute = 'ben', attributeType=1, enddate = convert(datetime,'99990101') union all
select entity = 1, attribute = 'alt', attributeType=2, enddate = convert(datetime,'99990101') union all
select entity = 1, attribute = '12345', attributeType=3, enddate = convert(datetime,'99990101') union all
select entity = 2, attribute = 'sam', attributeType=1, enddate = convert(datetime,'99990101') union all
select entity = 2, attribute = 'smith', attributeType=2, enddate = convert(datetime,'99990101') union all
select entity = 2, attribute = '67890', attributeType=3, enddate = convert(datetime,'99990101') union all
select entity = 2, attribute = '68790', attributeType=3, enddate = convert(datetime,'20130331') union all
select entity = 2, attribute = '876', attributeType=3, enddate = convert(datetime,'19810101')
)
select top 1
FirstName, LastName, AccountNum
from (
select top 1
a1.entity, FirstName, LastName
from (
select entity, enddate, attribute as FirstName
from data d
where d.enddate >= getdate()
and attributeType = 1
) a1
join (
select entity, enddate, attribute as LastName
from data
where enddate >= getdate()
and attributeType = 2
) a2 on a1.entity = a2.entity
and a1.enddate = a2.enddate
where FirstName = 'sam' and LastName = 'smith'
and a1.enddate >= getdate() and a2.enddate >= getdate()
order by a1.enddate
) E
left join (
select entity, enddate, attribute as AccountNum
from data
where enddate >= getdate()
and attributeType = 3
) a3 on a3.entity = E.entity
order by a3.enddate
returning:
FirstName LastName AccountNum
--------- -------- ----------
sam smith 68790
Note that it is quite common for accountign departments, at least, to enter future transactions during quiet times of the month, especially if those transactions will take effect during busy times of the month (ie month-end). The same for annual transactions. One should not assume that only one record can exist with an expiry > getdate().