Using data from tables in a group by - sql

Question

names:
id, first, last
879 Scotty Anderson
549 Melvin Anderson
554 Freddy Appleton
321 Grace Appleton
112 Milton Appleton
189 Jackson Black
99 Elizabeth Black
298 Jordan Frey
parents:
id, student_id
549 879
321 554
112 554
99 189
298 189
Expected Output
(without the 'Student:' / 'Parent:')
Student: Anderson, Scotty
Parent: Anderson, Melvin
Student: Appleton, Freddy
Parent: Appleton, Grace
Parent: Appleton, Milton
Student: Black, Jackson
Parent: Black, Elizabeth
Parent: Frey, Jordan
Using the data above, how can I achieve the expected output?
I currently use SQL similar to this to get a list of current students and names.
select b.last, b.first
from term a, names b
where a.id = b.id(+)
order by b.last
Which returns:
Anderson, Scotty
Appleton, Freddy
Black, Jackson
My question is how to take the parents table and add to this query so it has this output:
Anderson, Scotty
Anderson, Melvin
Appleton, Freddy
Appleton, Grace
Appleton, Milton
Black, Jackson
Black, Elizabeth
Frey, Jordan

Answer 1

The idea in a query like this is to break the data down into something that helps you solve the problem, and then put it back together as needed. In this case I'm going to make use of common table expressions, which allows me to treat queries as tables and then recombine them handily.
Looking at the desired results it looks like we want to have the students appear first, followed by their mothers (ladies first :-), and then their fathers. So, OK, let's figure out how to extract the needed data. We can get the students and their associated data pretty simply:
select distinct p.student_id as student_id,
n.first,
n.last,
0 as type
from parents p
inner join names n
on n.id = p.student_id
The type column, with its constant value of zero, is just used to identify that this is a student. (You'll see why in a minute).
Now, getting the mother's is a bit more difficult because we don't have any gender information to use. However, we'll use what we have, which is names. We know that names like Melvin, Milton, and Jordan are "guy" names. (Yes, I know Jordan can be a girls name too. My daughter has a male coach named Jordan, and a female teammate named Jordan. Just go with it - for purposes of argument in this case Jordan is a guys name, 'K? 'K :-). So we'll use that information to help us identify the mom's:
select p.student_id, n.first, n.last, 1 as type
from parents p
inner join names n
on n.id = p.id
where first not in ('Melvin', 'Milton', 'Jordan')
Notice here that we assign the value of 1 to the type column for mothers.
Similarly, we'll find the dads:
select p.student_id, n.first, n.last, 2 as type
from parents p
inner join names n
on n.id = p.id
where first in ('Melvin', 'Milton', 'Jordan')
And here we assign a value of 2 for the type.
OK - given the above we just need to combine the data properly. We don't want to use a JOIN, however, because we want the names to get spit out one after the other from the query - and the way we do THAT in SQL is with the UNION or UNION ALL operator. (Generally, you're going to want to use UNION ALL, because UNION will check the result set to ensure there are no duplicates - which in the case of a large result set takes, oh, more or less FOREVER!). And so, the final query looks like:
with all_students as (select distinct p.student_id as student_id,
n.first,
n.last,
0 as type
from parents p
inner join names n
on n.id = p.student_id),
all_mothers as (select p.student_id, n.first, n.last, 1 as type
from parents p
inner join names n
on n.id = p.id
where first not in ('Melvin', 'Milton', 'Jordan')),
all_fathers as (select p.student_id, n.first, n.last, 2 as type
from parents p
inner join names n
on n.id = p.id
where first in ('Melvin', 'Milton', 'Jordan'))
select last || ', ' || first as name from
(select * from all_students
union all
select * from all_mothers
union all
select * from all_fathers)
order by student_id desc, type;
We just take the student data, followed by the mom data, followed by the dad data, then sort it by the student ID from highest to lowest (I just looked at the desired results to figure out that this should be a descending sort), and then by the type (which results in the student (type=0) being first, following by their mother (type=1) and then their father (type=2)).
SQLFiddle here
Share and enjoy.

Answer 2

generic SQL, mmmmm I'd like there to be A generic SQL :)
First off you want to stop using the antique (+) join syntax that is exclusive to Oracle
select b.last, b.first
from term a
LEFT OUTER JOIN names b ON a.id = b.id
order by b.last
That is way more generic! (nb: You can abbreviate to just LEFT JOIN)
Now to concatenate (Last Name comma space First Name) there are options some not generic
SQL Server/MySQL and others supporting CONCAT()
select CONCAT(b.last , ', ', b.first)
from term a
LEFT OUTER JOIN names b ON a.id = b.id
order by b.last
not all versions of Oracle or SQL Server support CONCAT()
Oracle's concat() only takes 2 parameters; grrrrr
ORACLE
select b.last || ', ' || b.first
from term a
LEFT OUTER JOIN names b ON a.id = b.id
order by b.last
In this form Oracle generally handles data type conversions automatically (I think, please check on date/timestamps maybe others)
TSQL (Sybase, MS SQL Server)
select b.last + ', ' + b.first
from term a
LEFT OUTER JOIN names b ON a.id = b.id
order by b.last
In this form you must explicitly cast/convert data types to n|var|char for concatenation if not already a string type
For your list of concatenated names:
You need in addition to the last name a method to retain the family group together, plus distinguish between student and parent. As you want just one column of names this indicates you need a column of id's that point to the last and first names. So making some assumptions about the table TERM my guess is you list the students from that, then append the parents that relate to that group of students, and finally to output the required list in the required order.
select
case when type = 1 then 'Student' else 'Parent' end as who
, names.last || ', ' || names.first as Name
from (
select
STUDENT_ID as name_id
, STUDENT_ID as family_id
, 1 as TYPE
from term
union all
select
PARENTS.ID as name_id
, PARENTS.STUDENT_ID as family_id
, 2 as TYPE
from PARENTS
inner join term on PARENTS.STUDENT_ID = term.STUDENT_ID
) sq
inner join NAMES ON sq.name_id = NAMES.ID
order by
names.last
, sq.family_id
, sq.type
see: http://sqlfiddle.com/#!4/01804/6

Answer 3

This is too long for a comment.
Your question doesn't make sense. The easy answer to the question is:
select last, first
from names;
But it seems unlikely that is what you want.
Your sample query mentions a table term. That is not mentioned elsewhere in the question. Please clarify the question or delete this one and ask another.

Answer 4

I think I see what you're trying to do. I think you could set up a derived table and then query it. Set up something like: case when student id= id then 1 else 0 as match or whatever. Then query your derived table and group by match.

Answer 5

I would do it like that in SQL:
Select last +', '+ first as fullname from names;