I'm trying to write a query that puts some results (in my case a single result) at the top, and then sorts the rest. I have yet to find a PostgreSQL solution.
Say I have a table called airports like so.
id | code | display_name
----+------+----------------------------
1 | SDF | International
2 | INT | International Airport
3 | TES | Test
4 | APP | Airport Place International
In short, I have a query in a controller method that gets called asynchronously when a user text searches for an airport either by code or display_name. However, when a user types in an input that matches a code exactly (airport code is unique), I want that result to appear first, and all airports that also have int in their display_name to be displayed afterwards in ascending order. If there is no exact match, it should return any wildcard matches sorted by display_name ascending. So if a user types in INT, The row (2, INT, International Airport) should be returned first followed by the others:
Results:
1. INT | International Airport
2. APP | Airport Place International
3. SDF | International
Here's the kind of query I was tinkering with that is slightly simplified to make sense outside the context of my application but same concept nonetheless.
SELECT * FROM airports
WHERE display_name LIKE 'somesearchtext%'
ORDER BY (CASE WHEN a.code = 'somesearchtext` THEN a.code ELSE a.display_name END)
Right now the results if I type INT I'm getting
Results:
1. APP | Airport Place International
2. INT | International Airport
3. SDF | International
My ORDER BY must be incorrect but I can't seem to get it
Any help would be greatly appreciated :)
If you want an exact match on code to return first, then I think this does the trick:
SELECT a.*
FROM airports a
WHERE a.display_name LIKE 'somesearchtext%'
ORDER BY (CASE WHEN a.code = 'somesearchtext' THEN 1 ELSE 2 END),
a.display_name
You could also write this as:
ORDER BY (a.code = 'somesearchtext') DESC, a.display_name
This isn't standard SQL, but it is quite readable.
I think you can achieve your goal by using a UNION.
First get an exact match and then add that result to rest of the data as you which.
e.g.. (you will need to work in this a bit)
SELECT * FROM airports
WHERE code == 'somesearchtext'
ORDER BY display_name
UNION
SELECT * FROM airports
WHERE code != 'somesearchtext' AND display_name LIKE 'somesearchtext%'
ORDER BY display_name
Related
I am trying to extract the country code prefix from a list of numbers, and match them to the region that they belong to. The data might look something like this:
| id | phone_number |
|----|----------------|
| 1 | +27000000000 |
| 2 | +16840000000 |
| 3 | +10000000000 |
| 4 | +27000000000 |
The country codes here are:
American Samoa: +1684
United States and Caribbean: +1
South Africa: +27
And the desired result would be something this:
| country | count |
|-----------------------------|-------|
| South Africa | 2 |
| American Samoa | 1 |
| United States and Caribbean | 1 |
There are some difficulties because
country prefix codes vary from 1 to 4 numbers and even without the country prefix,
phone number length varies from place to place.
I do not have write access to this DB, so adding another column, while probably the best solution, will not work in this use case
This is my current solution:
SELECT
CASE
WHEN SUBSTRING(phone_number,1,5) = '+1684' THEN 'American Samoa'
WHEN SUBSTRING(phone_number,1,5) = '+1264' THEN 'Anguilla'
...
WHEN SUBSTRING(phone_number,1,5) = '+1599' THEN 'Saint Martin'
WHEN SUBSTRING(phone_number,1,4) = '+355' THEN 'Albania'
WHEN SUBSTRING(phone_number,1,4) = '+213' THEN 'Algeria'
...
WHEN SUBSTRING(phone_number,1,4) = '+263' THEN 'Zimbabwe'
WHEN SUBSTRING(phone_number,1,3) = '+93' THEN 'Afghanistan'
WHEN SUBSTRING(phone_number,1,3) = '+54' THEN 'Argentina'
...
WHEN SUBSTRING(phone_number,1,3) = '+58' THEN 'Venezuela'
WHEN SUBSTRING(phone_number,1,3) = '+84' THEN 'Vietnam'
WHEN SUBSTRING(phone_number,1,2) = '+1' THEN 'United States and Caribbean'
WHEN SUBSTRING(phone_number,1,2) = '+7' THEN 'Kazakhstan, Russia'
ELSE 'unknown'
END as country_name,
count(*)
FROM users
GROUP BY country_name
order by count desc
There are ~205 WHEN ... THEN cases. It seems to be very inefficient and times out. I assume this is because it runs the pattern matching on every row. This would need to scale to roughly 10s of millions of rows
Is there a more efficient way to do this?
I am using postgreSQL 9.6.16
In spite of reading the whole table, an index could help here. In order to aggregate the data per country code, the DBMS must sort all rows by country code. Sorting is an expensive operation, especially on large data sets. If you had an index on the country codes, the DBMS would find the codes already pre-sorted in the index and could avoid the work of sorting the data.
You don't have the separate country code in a column, but each phone number starts with the code, so you could index the complete phone number:
create index idx on users (phone_number);
Then you must make it obvious to the DBMS that you are interested in the beginnings of the string, so it will consider using the index. Invoking a function like SUBSTRING on the phone number is likely to make the the DBMS blind to this. Use LIKE instead. According to the docs (https://www.postgresql.org/docs/9.3/indexes-types.html), indexes on strings can be used with LIKE 'something%':
WHEN phone_number LIKE '+1684%' THEN 'American Samoa'
There is no guarantee this will help, but it's worth a try I think. It depends on whether the optimizer sees the advantage of using the pre-sorted phone numbers from the index.
I take a Database course in which we have listings of AirBnBs and need to be able to do some SQL queries in the Relationship-Model we made from the data, but I struggle with one in particular :
I have two tables that we are interested in, Billing and Amenities. The first one have the id and price of listings, the second have id and wifi (let's say, to simplify, that it equals 1 if there is Wifi, 0 otherwise). Both have other attributes that we don't really care about here.
So the query is, "What is the difference in the average price of listings with and without Wifi ?"
My idea was to build to JOIN-tables, one with listings that have wifi, the other without, and compare them easily :
SELECT avg(B.price - A.price) as averagePrice
FROM (
SELECT Billing.price, Billing.id
FROM Billing
INNER JOIN Amenities
ON Billing.id = Amenities.id
WHERE Amenities.wifi = 0
) A, (
SELECT Billing.price, Billing.id
FROM Billing
INNER JOIN Amenities
ON Billing.id = Amenities.id
WHERE Amenities.wifi = 1) B
WHERE A.id = B.id;
Obviously this doesn't work... I am pretty sure that there is a far easier solution to it tho, what do I miss ?
(And by the way, is there a way to compute the absolute between the difference of price ?)
I hope that I was clear enough, thank you for your time !
Edit : As mentionned in the comments, forgot to say that, but both tables have idas their primary key, so that there is one row per listing.
Just use conditional aggregation:
SELECT AVG(CASE WHEN a.wifi = 0 THEN b.price END) as avg_no_wifi,
AVG(CASE WHEN a.wifi = 1 THEN b.price END) as avg_wifi
FROM Billing b JOIN
Amenities a
ON b.id = a.id
WHERE a.wifi IN (0, 1);
You can use a - if you want the difference instead of the specific values.
Let's assume we're working with data like the following (problems with your data model are noted below):
Billing
+------------+---------+
| listing_id | price |
+------------+---------+
| 1 | 1500.00 |
| 2 | 1700.00 |
| 3 | 1800.00 |
| 4 | 1900.00 |
+------------+---------+
Amenities
+------------+------+
| listing_id | wifi |
+------------+------+
| 1 | 1 |
| 2 | 1 |
| 3 | 0 |
+------------+------+
Notice that I changed "id" to "listing_id" to make it clear what it was (using "id" as an attribute name is problematic anyways). Also, note that one listing doesn't have an entry in the Amenities table. Depending on your data, that may or may not be a concern (again, refer to the bottom for a discussion of your data model).
Based on this data, your averages should be as follows:
Listings with wifi average $1600 (Listings 1 and 2)
Listings without wifi (just 3) average 1800).
So the difference would be $200.
To achieve this result in SQL, it may be helpful to first get the average cost per amenity (whether wifi is offered). This would be obtained with the following query:
SELECT
Amenities.wifi AS has_wifi,
AVG(Billing.price) AS avg_cost
FROM Billing
INNER JOIN Amenities ON
Amenities.listing_id = Billing.listing_id
GROUP BY Amenities.wifi
which gives you the following results:
+----------+-----------------------+
| has_wifi | avg_cost |
+----------+-----------------------+
| 0 | 1800.0000000000000000 |
| 1 | 1600.0000000000000000 |
+----------+-----------------------+
So far so good. So now we need to calculate the difference between these 2 rows. There are a number of different ways to do this, but one is to use a CASE expression to make one of the values negative, and then simply take the SUM of the result (note that I'm using a CTE, but you can also use a sub-query):
WITH
avg_by_wifi(has_wifi, avg_cost) AS
(
SELECT Amenities.wifi, AVG(Billing.price)
FROM Billing
INNER JOIN Amenities ON
Amenities.listing_id = Billing.listing_id
GROUP BY Amenities.wifi
)
SELECT
ABS(SUM
(
CASE
WHEN has_wifi = 1 THEN avg_cost
ELSE -1 * avg_cost
END
))
FROM avg_by_wifi
which gives us the expected value of 200.
Now regarding your data model:
If both your Billing and Amenities table only have 1 row for each listing, it makes sense to combine them into 1 table. For example: Listings(listing_id, price, wifi)
However, this is still problematic, because you probably have a bunch of other amenities you want to model (pool, sauna, etc.) So you might want to model a many-to-many relationship between listings and amenities using an intermediate table:
Listings(listing_id, price)
Amenities(amenity_id, amenity_name)
ListingsAmenities(listing_id, amenity_id)
This way, you could list multiple amenities for a given listing without having to add additional columns. It also becomes easy to store additional information about an amenity: What's the wifi password? How deep is the pool? etc.
Of course, using this model makes your original query (difference in average cost of listings by wifi) a bit tricker, but definitely still doable.
I'm trying to implement a cursor-based paginating list based off of data from a Postgres database.
As an example, say I have a table with the following columns:
id | firstname | lastname
I want to paginate this data, which would be pretty simple if I only ever wanted to sort it by the id, but in my case, I want the option to sort by last name, and there's guaranteed to be multiple people with the same last name.
If I have a select statement like follows:
SELECT * FROM people
ORDER BY lastname ASC;
In the case, I could make my encoded cursor contain information about the lastname so I could pick up where I left off, but since there will be multiple users with the same last name, this will be buggy. Is there a way in SQL to only get the results after a certain id in an ordered list where it is not the column by which the results are sorted?
Example results from the select statement:
1 | John | Doe
4 | John | Price
2 | Joe | White
6 | Jim | White
3 | Sam | White
5 | Sally | Young
If I wanted a page size of 3, I couldn't add WHERE lastname <= :lastname as I'd have duplicate data on the list since it would return ids 2, 6, and 3 during that call. In my case, it'd be helpful if I could add to my query something similar to AFTER id = 6 where it could skip everything until it finds that id in the ordered list.
Yes. If I understand correctly:
select t.*
from t
where (lastname, id) > (select t2.lastname, t2.id
from t t2
where t2.id = ?
)
order by t.lastname;
I think I would add firstname into the mix, but it is the same idea.
Limit and offset are used for pagination e.g.:
SELECT id, lastname, firstname FROM people
Order by lastname, firstname, id
Offset 0
Limit 10
This will bring you the first to the 10th row, to retrieve the next page you need to specify the offset to 10
Here the documentation:
https://www.postgresql.org/docs/9.6/static/queries-limit.html
I have a question for you all. I have 'inherited' a DB at work and I have to create a report from a table using different conditions. Please note I'm no sql expert, I hope what I write makes sense.
Trying to simplify, I have a HARDWARE table that contains the following:
HWTYPE - type of hardware
HWMODEL - model of hardware
PHONENUM - phone number
USERID - user the hardware is assigned to
the data looks like this:
HWTYPE | HWMODEL | PHONENUM | USERID
-------+------------+------------+----------
SIM | SIMVOICE | 123456 | CIRO
SIM | SIMVOICE | 124578 | LEO
PHONE | APPLE | | CIRO
PHONE | SAMSUNG | | LEO
now as you can see, every user has assigned one phone and one SIM with a phone number.
I need to sort the data per user, so that every line of the query result look like:
HW | PHONENUM | USERID
---------+--------------+------
APPLE | 123456 | CIRO
SAMSUNG | 124578 | LEO
so basically: group column PHONENUM and HWMODEL based on USER.
And this is where I get stuck! I tried union, join, case etc. but I still don't get the correct result.
Again apologies for the (probably) very basic question. I tried to look for something similar but could not find anything.
Thanks to whoever will want to help me.
regards
Leo
I dont know that I understood your question or not
But i think you just need to write following query for your O/P
SELECT
HWTYPE, HWMODEL, USERID
FROM
HARDWARE
GROUP BY USERID ,HWTYPE,HWMODEL
ORDER BY HWTYPE
Placing my comment as an answer;
Write this as your SQL:
SELECT
(HWTYPE, HWMODEL, USERID)
FROM
HARDWARE
GROUP BY (USERID) /*Other Clauses can be added here, but ensure you use commas to seperate them!*/
Taking this step by step:
SELECT ... -> what columns you want to see
FROM ... -> what table you want it from (use joins if you need from multiple tables)
GROUP BY... -> What you want to collect together
There is also:
WHERE... -> conditions for when to include/what not to include
You can also get your expected Result using below query. This will use self join on Hardware table as well as reduce the length of query syntex.
SELECT H2.HWMODEL AS HW,H1.PHONENUM,H1.USERID FROM HARDWARE H1 INNER JOIN HARDWARE H2 ON H1.USERID = H2.USERID
WHERE ISNULL(H1.PHONENUM,'') <> ''
AND ISNULL(H2.PHONENUM,'') = ''
ORDER BY H2.HWMODEL ASC
Hope this will help you.
If your goal is a list of Phone numbers and models sorted by user, you can use this query:
SELECT HWMODEL,PHONENUM,USERID FROM HARDWARE ORDER BY USER
Hope to have understood your question
SELECT
hw.HWMODEL as HW
,phone.PHONENUM
,user.USERID
FROM
(
SELECT DISTINCT
USERID
FROM
HARDWARE
) as user
LEFT JOIN
(
SELECT
USERID
,PHONENUM
FROM
HARDWARE
WHERE
PHONENUM IS NOT NULL
) as phone
ON phone.USERID = user.USERID
LEFT JOIN
(
SELECT
USERID
,HWMODEL
FROM
HARDWARE
WHERE
HWTYPE = 'PHONE'
) AS hw
ON hw.USERID = user.USERID
ORDER BY
user.USERID
,hw.HWMODEL
Basically, I'm dealing with a horribly set up table that I'd love to rebuild, but am not sure I can at this point.
So, the table is of addresses, and it has a ton of similar entries for the same address. But there are sometimes slight variations in the address (i.e., a room # is tacked on IN THE SAME COLUMN, ugh).
Like this:
id | place_name | place_street
1 | Place Name One | 1001 Mercury Blvd
2 | Place Name Two | 2388 Jupiter Street
3 | Place Name One | 1001 Mercury Blvd, Suite A
4 | Place Name, One | 1001 Mercury Boulevard
5 | Place Nam Two | 2388 Jupiter Street, Rm 101
What I would like to do is in SQL (this is mssql), if possible, is do a query that is like:
SELECT DISTINCT place_name, place_street where [the first 4 letters of the place_name are the same] && [the first 4 characters of the place_street are the same].
to, I guess at this point, get:
Plac | 1001
Plac | 2388
Basically, then I can figure out what are the main addresses I have to break out into another table to normalize this, because the rest are just slight derivations.
I hope that makes sense.
I've done some research and I see people using regular expressions in SQL, but a lot of them seem to be using C scripts or something. Do I have to write regex functions and save them into the SQL Server before executing any regular expressions?
Any direction on whether I can just write them in SQL or if I have another step to go through would be great.
Or on how to approach this problem.
Thanks in advance!
Use the SQL function LEFT:
SELECT DISTINCT LEFT(place_name, 4)
I don't think you need regular expressions to get the results you describe. You just want to trim the columns and group by the results, which will effectively give you distinct values.
SELECT left(place_name, 4), left(place_street, 4), count(*)
FROM AddressTable
GROUP BY left(place_name, 4), left(place_street, 4)
The count(*) column isn't necessary, but it gives you some idea of which values might have the most (possibly) duplicate address rows in common.
I would recommend you look into Fuzzy Search Operations in SQL Server. You can match the results much better than what you are trying to do. Just google sql server fuzzy search.
Assuming at least SQL Server 2005 for the CTE:
;with cteCommonAddresses as (
select left(place_name, 4) as LeftName, left(place_street,4) as LeftStreet
from Address
group by left(place_name, 4), left(place_street,4)
having count(*) > 1
)
select a.id, a.place_name, a.place_street
from cteCommonAddresses c
inner join Address a
on c.LeftName = left(a.place_name,4)
and c.LeftStreet = left(a.place_street,4)
order by a.place_name, a.place_street, a.id