As a personal education experiment, I am building a database for an imaginary animal shelter. I am quite new to SQL and databases in general.
Task: Finding all the owners of a pet in an animal shelter database.
I have three tables: Pets, Owners, and Pets2Owners. Owners can have one or many pets, and pets can have one, many, or no owners. The tables look like this:
Pets
+--------+----------+
| ID | Name |
+--------+----------+
| 1 | Opal |
| 2 | Fuzzy |
| 3 | Angel |
| 4 | Peewee |
| 5 | Spike |
+--------+----------+
Owners
+----------+--------+
| ID | Name |
+----------+--------+
| 1 | Shy |
| 2 | Belle |
| 3 | Velvet |
| 4 | Brilla |
+----------+--------+
Pets2Owners
+----+--------+----------+
| ID | Pet_ID | Owner_ID |
+----+--------+----------+
| 1 | 1 | 2 |
| 2 | 2 | 1 |
| 3 | 3 | 1 |
| 4 | 5 | 3 |
| 5 | 5 | 4 |
+----+--------+----------+
So, from Pets2Owners, we see that Pet #3 (Angel) is owned by Owner #1 (Ms. Shy), Pet #5 (Spike) is owned by both Owners #3 & 4 (Velvet and Brilla), and Pet #4 (Peewee) is owned by no one.
I an inexperienced in SQL, and I'm not sure this is possible, but is there a way to make a single query that gives me all the information on pets and owners without duplicating pets, like this:
+--------+--------+
| Pets | Owners |
+--------+--------+
| Opal | Belle |
| Fuzzy | Shy |
| Angel | Shy |
| Peewee | (none) |
| Spike | Velvet |
| | Brilla |
+--------+--------+
Essentially, I want a way to combine information from all three tables into one. I have tried using joins, but they leave me with duplicate entries (e.g. two rows for Spike, one with the owner Velvet, the other with the owner Brilla).
Alternately, is it possible to make a query that would return all the owners of a particular pet, like so:
Spike's Owners
+--------+
| Owners |
+--------+
| Velvet |
| Brilla |
+--------+
I could use this to accomplish the same goal and have all the owners of a particular pet listed (although I'm not sure if SQL has variables that would let me make a single query for a variable PetName, then repeat it for a arbitrary name)
You can use Allen Browne's function ConcatRelated() to create a single row like this:
| Spike | Velvet, Brilla |
ConcatRelated() is designed for one-to-many relationships. Since you have many-to-many, you need an intermediate query that combines Pet IDs with Owner names:
SELECT Pets2Owners.Pet_ID, Owners.OwnerName
FROM Pets2Owners INNER JOIN Owners ON Pets2Owners.Owner_ID = Owners.ID;
I called this query Pet_OwnerNames.
Then ConcatRelated() is straightforward:
SELECT Pets.PetName,
ConcatRelated("OwnerName", "Pet_OwnerNames", "Pet_ID = " & ID) AS Owners
FROM Pets;
Result:
+---------+----------------+
| PetName | Owners |
+---------+----------------+
| Opal | Belle |
| Fuzzy | Shy |
| Angel | Shy |
| Peewee | |
| Spike | Velvet, Brilla |
+---------+----------------+
SELECT Pets.Name AS Pets, Owners.Name AS Owner
FROM Pets2Owner INNER JOIN Pets ON Pets2Owner.[Pet Id] = Pets.[id]
INNER JOIN Owners ON Pets2Owner.[Owner Id] = Owners.[id]
after you get a good grip of the JOINS,
try to look at parameters for Access :)
Related
I'm trying to merge 2 queries into 1 (cuts the number of daily queries in half): I have 2 tables, I want to do a query against 1 table, then the same query against the other table that has the same list just less entries.
Basically its a list of (let's call it for obfuscation) people and hobby. One table is ALL people & hobby, the other shorter list is people & hobby that I've met. Table 2 would all be found in table 1. Table 1 includes entries (people I have yet to meet) not found in table 2
The tables are synced up from elsewhere, what I'm looking to do is print a list of ALL people in the first column then print the hobby ONLY of people that are on both lists. That way I can see the lists merged, and track the rate at which the gap between both lists is closing. I have tried a number of SQL combinations but they either filter out the first table and match only items that are true for both (i.e. just giving me table 2) or just adding table 2 to table 1.
Example of what I'm trying to do below:
+---------+----------+--+----------+---------+--+---------+----------+
| table1 | | | table2 | | | query | |
+---------+----------+--+----------+---------+--+---------+----------+
| name | hobby | | activity | person | | name | hobby |
| bob | fishing | | fishing | bob | | bob | fishing |
| bill | vidgames | | hiking | sarah | | bill | |
| sarah | hiking | | planking | sabrina | | sarah | hiking |
| mike | cooking | | | | | mike | |
| sabrina | planking | | | | | sabrina | planking |
+---------+----------+--+----------+---------+--+---------+----------+
Normally I'd just take the few days to learn SQL a bit better however I'm stretched pretty thin at work as it is!
I should mention the table 2 is flipped and the headings are all unique (don't think this matters)!
I think you just want a left join:
select t1.name, t2.activity as hobby
from table1 t1 left join
table2 t2
on t1.name = t2.person;
I am very new to database design and am using MS Access to try achieve my task. I am trying to create a database design that will allow for the name and description of two items to be queried
on a single row of information. Here is the problem: certain items are converted to other particular items -
any item can have multiple conversions performed on it, and all conversions will have two (many) items involved.
In this sense, we have a many-to-many relationship which necessitates the use of an intermediate table. My
tables must be structured in a way that allows for me to, in one row, query the Item ID's and names
of which items were involved in conversions.
My current table layout is as follows:
Items
+--------+----------+------------------+--+
| ItemID*| ItemName | ItemDescription | |
+--------+----------+------------------+--+
| 1 | DESK | WOOD, 4 LEG | |
| 2 | SHELF | WOOD, SOLID BASE | |
| 3 | TABLE | WOOD, 4 LEG | |
+--------+----------+------------------+--+
ItemConversions
+------------------+--------------+
| ConversionID(CK) | Item1_ID(CK) |
+------------------+--------------+
| 1 | 2 |
| 2 | 2 |
| 3 | 1 |
+------------------+--------------+
Conversions
+---------------+----------+----------+
| ConversionID* | Item1_ID | Item2_ID |
+---------------+----------+----------+
| 1 | 2 | 1 |
| 2 | 2 | 3 |
| 3 | 1 | 3 |
+---------------+----------+----------+
What I want is for it to be possible to achieve the kind of query I described above, though I don't think
my current layout is going to work for this, since the tables are only being joined on Item1_ID. Any advice
would be appreciated, hopefully my tables are not too specific and this is easily understandable.
A sample query output might look like this:
+--------------+----------+----------+----------+----------+
| ConversionID | Item1_ID | ItemName | Item2_ID | ItemName |
+--------------+----------+----------+----------+----------+
| 1 | 2 | SHELF | 1 | DESK |
+--------------+----------+----------+----------+----------+
I got it working how I wanted to with the help of June7's suggestion - I didn't know you could add in tables
multiple times in the query design page (very useful!). As for the tables, I edited the layout so that I have only
Items and Conversions (I deleted ItemConversions). Using the AS sql command I was able to write a query that pulls
the data I want from the tables. The table and query layout can be seen below:
Items
+--------+----------+------------------+--+
| ItemID*| ItemName | ItemDescription | |
+--------+----------+------------------+--+
| 1 | DESK | WOOD, 4 LEG | |
| 2 | SHELF | WOOD, SOLID BASE | |
| 3 | TABLE | WOOD, 4 LEG | |
+--------+----------+------------------+--+
Conversions
+---------------+----------+----------+
| ConversionID* | Item1_ID | Item2_ID |
+---------------+----------+----------+
| 1 | 2 | 1 |
| 2 | 2 | 3 |
| 3 | 3 | 1 |
+---------------+----------+----------+
Query:
SELECT
Conversions.ConversionID,
Conversions.Item1_ID,
Conversions.Item2_ID,
Items.ItemName,
Items_1.ItemName,
FROM
(
Conversions
INNER JOIN
Items
ON Conversions.Item1_ID = Items.ItemID
)
INNER JOIN
Items AS Items_1
ON Conversions.Item2_ID = Items_1.ItemID;
I am trying to filter a set of tables that includes an M:N junction table in Android Room (SQLite).
An image can have many subjects. I'd like to allow filtering by a subject, so that I get a row with complete image information (including all subjects). So if an image had (National Park, Yosemite) filtering for either would result in one row with both keywords. Unless I messed something up, a typical join will result in multiple rows such that matching Yosemite would get the right image, but you'd be lacking National Park. I came up with this:
SELECT *,
(SELECT GROUP_CONCAT(name)
FROM meta_subject_junction
JOIN subject
ON subject.id = meta_subject_junction.subjectId
WHERE meta_subject_junction.metaId = meta.id) AS keywords,
(SELECT documentUri
FROM image_parent
WHERE meta.parentId = image_parent.id ) AS parentUri
FROM meta
Now this gets me the complete rows, but I think at this point I'd need to:
WHERE keywords LIKE(%YOSEMITE%)
and I think the LIKE is less than ideal, not to mention an imprecise match. Is there a better way to accomplish this? Thanks, this is bending my novice SQL brain.
Further details
meta
+----+----------+--+
| id | name | |
+----+----------+--+
| 1 | yosemite | |
| 2 | bryce | |
| 3 | flowers | |
+----+----------+--+
subject
+----+---------------+--+
| id | name | |
+----+---------------+--+
| 1 | National Park | |
| 2 | Yosemite | |
| 3 | Tulip | |
+----+---------------+--+
junction
+--------+-----------+
| metaId | subjectId |
+--------+-----------+
| 1 | 1 |
| 1 | 2 |
| 2 | 1 |
| 3 | 3 |
+--------+-----------+
Although I may have done something wrong, as far as I can tell Android Room doesn't like:
+----+-----------+---------------+
| id | name | subject |
+----+-----------+---------------+
| 1 | yosemite | National Park |
| 1 | yosemite | Yosemite |
+----+-----------+---------------+
so I'm trying to reduce the rows:
+----+-----------+-------------------------+
| id | name | subject |
+----+-----------+-------------------------+
| 1 | yosemite | National Park, Yosemite |
+----+-----------+-------------------------+
which the above query does. However, I also want to query for a subject. So that National Park filter will yield:
+----+-----------+-------------------------+
| id | name | subject |
+----+-----------+-------------------------+
| 1 | yosemite | National Park, Yosemite |
| 2 | bryce | National Park |
+----+-----------+-------------------------+
I'd like to be more precise/efficient than LIKE with the already 'concat' subject. Most of my attempts end up with no results in Room (multi-row) or reducing the subject to only the filter keyword.
Update
Here's a test I've been using to compare the actual SQL results from a query to what Android Room ends up with:
http://sqlfiddle.com/#!7/0ac11/10/0
That join query is interpreted as four objects in Android Room, so I'm trying to reduce the rows, but retain the full subject results while filtering for any image containing the subject keyword.
If you want multiple keywords, then where and group by and having can be used:
select image_id
from image_subject
where subject_id in ('a', 'b', 'c') -- whatever
group by image-id
having count(distinct subject_id) = 3; -- same count as in `where`
This gets the result I need, though I'd love to hear a better option if this is particularly inefficient.
SELECT meta.*,
(SELECT GROUP_CONCAT(name)
FROM junction
JOIN subject
ON subject.id = junction.subjectId
WHERE junction.metaId = meta.id) AS keywords,
junction.subjectId
FROM meta
LEFT JOIN junction ON junction.metaId = meta.id
WHERE subjectId IN (1,2)
GROUP BY meta.id
+----+----------+------------------------+-----------+
| id | name | keywords | subjectId |
+----+----------+------------------------+-----------+
| 1 | yosemite | National Park,Yosemite | 2 |
| 2 | bryce | National Park | 1 |
+----+----------+------------------------+-----------+
http://sqlfiddle.com/#!7/86a76/13
Basically, I have 3 tables, titles, providers, and provider_titles.
Let's say they look like this:
| title_id | title_name |
|------------|----------------|
| 1 | San Andres |
| 2 |Human Centipede |
| 3 | Zoolander 2 |
| 4 | Hot Pursuit |
| provider_id| provider_name |
|------------|----------------|
| 1 | Hulu |
| 2 | Netflix |
| 3 | Amazon_Prime |
| 4 | HBO_GO |
| provider_id| title_id |
|------------|----------------|
| 1 | 1 |
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
| 3 | 3 |
| 4 | 4 |
So, clearly there are titles with multiple providers, yeah? Typical many-to-many so far.
So what I'm doing to query it is with a JOIN like the following:
SELECT * FROM provider_title JOIN provider ON provider_title.provider_id = provider.provider_id JOIN title ON title.title_id = provider_title.title_id WHERE provider.name IN ('Netflix', 'HBO_GO', 'Hulu', 'Amazon_Prime')
Ok, now to the actual issue. I don't want repeated title names back, but I do want all of the providers associated with the title. Let me explain with another table. Here is what I am getting back with the current query, as is:
| provider_id| provider_name | title_id | title_name |
|------------|---------------|----------|---------------|
| 1 | Hulu | 1|San Andreas |
| 1 | Hulu | 2|Human Centipede|
| 2 | Netflix | 1|San Andreas |
| 3 | Amazon_Prime | 1|San Andreas |
| 3 | Amazon_prime | 3|Zoolander 2 |
| 4 | HBO_GO | 4|Hot Pursuit |
But what I really want would be something more like
| provider_id| provider_name |title_id| title_name|
|------------|-----------------------------|--------|-----------|
| [1, 2, 3] |[Hulu, Netflix, Amazon_Prime]| 1|San Andreas|
Meaning I only want distinct titles back, but I still want each title's associated providers. Is this only possible to do post-sql query with logic iterating through the returned rows?
Depending on your database engine, there may be an aggregation function to help achieve this.
For example, this SQLfiddle demonstrates the postgres array_agg function:
SELECT t.title_id,
t.title_name,
array_agg( p.provider_id ),
array_agg( p.provider_name )
FROM provider_title as pt
JOIN
provider as p
ON pt.provider_id = p.provider_id
JOIN title as t
ON t.title_id = pt.title_id
GROUP BY t.title_id,
t.title_name
Other database engines have equivalents. For example:
mySQL has group_concat
Oracle has listagg
sqlite has group_concat (as well!)
If your database isn't covered by the above, you can google '[Your database engine] aggregate comma delimited string'
I've got sample data in database:
id (int) name (varchar) parts (varchar)
1 some_element wheel, bearing, hinge, servo
2 another_element bearing, servo, lift
3 third_element motor, wire
I want to filter results by parts. For example:
I'm typing wheel, servo - no results
I'm typing wheel, bearing, servo, hinge - returns some_element record
I'm typing bearing, servo, lift, wheel, bearing, hinge - it returns some_element and another_element
How to construct SQL query? Is there any other data type better for parts field?
Do some normalization so that you can write queries more easily and won't have such anomalies.
You'll need another structure, like:
The element table
+----+---------------+
| id | name |
+----+---------------+
| 1 | some_element |
+----+---------------+
| 2 | another_elem |
+----+---------------+
| 3 | third_elem |
+----+---------------+
The part table
+----+----------+
| id | name |
+----+----------+
| 1 | wheel |
+----+----------+
| 2 | bearing |
+----+----------+
| 3 | hinge |
+----+----------+
| 4 | servo |
+----+----------+
etc..
And another, such as element_parts to connect the other two by an m:n relation
+----+---------+---------+
| id | elem_id | part_id |
+----+----------+--------+
| 1 | 1 | 1 |
+----+---------+---------+
| 2 | 1 | 2 |
+----+---------+---------+
| 3 | 1 | 3 |
+----+---------+---------+
| 4 | 2 | 3 |
+----+---------+---------+
| 5 | 2 | 4 |
+----+---------+---------+
etc..
And now you can write a query to, say, filter elements that contain (or need) wheel and servo (adapting this question's accepted answer):
select *
from element e
where 2 = (
select count(distinct p.id)
from element_parts ep
inner join part p on p.id = ep.part_id
where p.name in ('wheel', 'servo')
and ep.elem_id = e.id
);