I have two tables which is
Student
ID
Name
Gender
Address
1
Abby
Girl
street
2
Mark
Boy
street
3
Lula
Girl
street
4
Bren
boy
street
Lessons
ID
Lessons_code
3
MK2234
5
22324KL
6
KCS233
and I want to join these tables then get the sum result of the students that didn't took a lesson then group it by gender like this:
Gender
total
Boy
2
girl
1
I know it use sum() and left outer join (?) but I don't know how to implement it.
I would suggest not exists:
select s.gender, count(*)
from students s
where not exists (select 1
from lessons l
where l.id = s.id
)
group by s.gender;
You have a very awkward data model. I would expect a column called lessons.id to refer to the primary key of the lessons table. Instead. it seems to refer to a student. A better name would be student_id.
I have question, I have hard time in solving a question on how to actually joining two table using inner join, where the return value shown must only be the unique value on both table.
For example: if table A contains:
ID Name
-------------------
1 Andy
2 Anthony
3 Sandy
And table B:
ID Job
----------------------
1 Student
1 Entrepreneur
3 CEO
It will return only Sandy as CEO and not returning ANDY with both jobs as student and entrepreneur.
Thanks a lot for your time and attention.
A simple join and aggregation would seem to work here:
SELECT a.ID, MAX(a.Name) AS Name, MAX(b.Job) AS Job
FROM TableA a
INNER JOIN TableB b
ON b.ID = a.ID
GROUP BY a.ID
HAVING COUNT(*) = 1;
Demo
The logic here is that the inner join filters off person in the A table not having any match at all in the B table. For those which do have matches, we retain single job match only by checking the count.
I'm working with 3 tables: actors, films, and actor_film. Actors and films only have 2 fields: id (primary key) and name. Actor_film also has 2 fields, actor and film, which are both foreign keys representing actor and film ids, respectively. So if a film had 4 actors in it, there'd be 4 actor_film entries with the same film and 4 different actors.
My problem is that, given a certain actor's id, I'd like to return the actor id, actor name, film name, and the total number of actors in that film. However, the only actors that I want to show are ones that contain certain letters in their names.
Let me clear things up with an example. Say Tom Hanks is in only 2 movies, Forrest Gump and Saving Private Ryan, and I'm looking for actors in those 2 movies that have "Gary" or "Matt" in their names. Further suppose that there are 4 actors in Forrest Gump, and 5 in Saving Private Ryan. Then, the only thing I'd want to return would be (without the column names, of course)
actor id | actor name | film name | # actors
abcdefg | Gary Sinise | Forrest Gump | 4
hijklmn | Matt Damon | Saving Private Ryan | 5
opqrstu | Paul Giamatti | Saving Private Ryan | 5
Currently, I'm 75% of the way there by using:
SELECT actor.id, actors.name, films.name,
FROM (
SELECT actor_film.film
FROM actor_film, actors
WHERE actor_film.actor = actors.id
) AS a, actor_film, actors, films
WHERE actor_film.film = a.film
AND actors.id = actor_film.actor
AND films.id = a.film;
This is returning stuff like:
arnie | Arnold Schwarzenegger | Around the World in 80 Days
arnie | Arnold Schwarzenegger | Around the World in 80 Days
for a film that has 2 actors in it. In other words, I can't pull out all the distinct actors in the movie, but get the proper count for it implicitly and not explicitly with COUNT.
Anyway, I think I'm looking for some kind of INNER JOIN or nested SELECT, but I'm new to SQLite3 and don't know how to bring these together. Any solutions would be great, and any explanations on top of that would be amazing as well.
You shouldn't use the old style joins. They were old in '95 when the newer standard that let you do left joins clearer was made a standard.
I've noticed you also use plurals for your table names (eg "actors") The standard style is to use the singular for the table table name (eg "actor")
I use both these suggestions below, I also show you each step. I suggest you run the queries for each step and look at the output to understand how everything works since you are new to SQL.
Ok, lets take you problem step by step. First of all to see each actor and the films they are in (your first 3 columns) do this:
SELECT a.id as actor_id, a.name as actor_name, f.name as film_name
FROM actor as a
JOIN actor_film af on a.id = af.actor
JOIN film as f on af.film = f.id
Your last column can be found with the following query:
SELECT af.film as film_id, count(*) as c
FROM actor_film as af
GROUP BY af.film
Now we just join them together
SELECT a.id as actor_id, a.name as actor_name, f.name as film_name, fc.c as num_actors
FROM actor as a
JOIN actor_film af on a.id = af.actor
JOIN film as f on af.film = f.id
JOIN (
SELECT af.film as film_id, count(*) as c
FROM actor_file as af
GROUP BY af.film
) as fc on af.film = fc.film_id
If you want you can add a
WHERE a.name = 'Gary' OR a.name = 'Matt'
depending on your platform you might want
WHERE lower(a.name) = 'gary' OR lower(a.name) = 'matt'
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
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.
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
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.
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.
I would do it like that in SQL:
Select last +', '+ first as fullname from names;
So let me preface this by saying that I'm not an SQL wizard by any means. What I want to do is simple as a concept, but has presented me with a small challenge when trying to minimize the amount of database queries I'm performing.
Let's say I have a table of departments. Within each department is a list of employees.
What is the most efficient way of listing all the departments and which employees are in each department.
So for example if I have a department table with:
id name
1 sales
2 marketing
And a people table with:
id department_id name
1 1 Tom
2 1 Bill
3 2 Jessica
4 1 Rachel
5 2 John
What is the best way list all departments and all employees for each department like so:
Sales
Tom
Bill
Rachel
Marketing
Jessica
John
Pretend both tables are actually massive. (I want to avoid getting a list of departments, and then looping through the result and doing an individual query for each department). Think similarly of selecting the statuses/comments in a Facebook-like system, when statuses and comments are stored in separate tables.
You can get it all in a single query with a simple join, e.g.:
SELECT d.name AS 'department', p.name AS 'name'
FROM department d
LEFT JOIN people p ON p.department_id = d.id
ORDER BY department
This returns all the data, but it's a bit of a pain to consume, since you'll have to iterate through every person anyway. You can go further and group them together:
SELECT d.name AS 'department',
GROUP_CONCAT(p.name SEPARATOR ', ') AS 'name'
FROM department d
LEFT JOIN people p ON p.department_id = d.id
GROUP BY department
You'll get something like this as the output:
department | name
-----------|----------------
sales | Tom, Bill, Rachel
marketing | Jessica, John
SELECT d.name, p.name
FROM department d
JOIN people p ON p.department_id = d.id
I suggest also reading a SQL Join tutorial or three. This is a very common and very basic SQL concept that you should understand thoroughly.
This is normally done in a single query:
SELECT DepartmentTable.Name, People.Name from DepartmentTable
INNER JOIN People
ON DepartmentTable.id = People.department_id
ORDER BY DepartmentTable.Name
This will suppress empty departments. If you want to show empty departments, change INNER to LEFT OUTER