Let's say I have this table:
id | status | type
----+--------+----------
1 | new | car
2 | new | boat
3 | used | car
4 | new | car
and I wanted to count all the new vehicles, and the number of cars in one go, how to do that?
I tried this:
SELECT COUNT(status='new'), COUNT(type='car') FROM table;
but it always counts to 4 (the total amount of rows). The only thing I can think of is using a CASE inside the COUNT, but is there a cleaner way?
You could use FILTER to perform conditional aggregation:
SELECT COUNT(*) FILTER(WHERE status='new'), COUNT(*) FILTER(WHERE type='car')
FROM tab;
Alternatively SUM:
SELECT SUM((status='new')::int), SUM((type='car')::int) FROM table;
Related
I need to count how many consultants are using a skill through a joining table (consultant_skills), and the challenge is to sum the children occurrences to the parents recursively.
Here's the reproduction of what I'm trying to accomplish. The current results are:
skill_id | count
2 | 2
3 | 1
5 | 1
6 | 1
But I need to compute the count to the parents recursively, where the expected result would be:
skill_id | count
1 | 2
2 | 2
3 | 1
4 | 2
5 | 2
6 | 1
Does anyone know how can I do that?
Sqlfiddle Solution
You need to use WITH RECURSIVE, as the Mike suggests. His answer is useful, especially in reference to using distinct to eliminate redundant counts for consultants, but it doesn't drive to the exact results you're looking for.
See the working solution in the sqlfiddle above. I believe this is what you are looking for:
WITH RECURSIVE results(skill_id, parent_id, consultant_id)
AS (
SELECT skills.id as skill_id, parent_id, consultant_id
FROM consultant_skills
JOIN skills on skill_id = skills.id
UNION ALL
SELECT skills.id as skill_id, skills.parent_id as parent_id, consultant_id
FROM results
JOIN skills on results.parent_id = skills.id
)
SELECT skill_id, count(distinct consultant_id) from results
GROUP BY skill_id
ORDER BY skill_id
What is happening in the query below the UNION ALL is that we're recursively joining the skills table to itself, but rotating in the previous parent id as the new skill id, and using the new parent id on each iteration. The recursion stops because eventually the parent id is NULL and there is no JOIN because it's an INNER join. Hope that makes sense.
I have a table that has 3 columns.
id | name | score | approve
--------------------
1 | foo | 90 | f
2 | foo | 80 | t
I want to
SELECT id WHERE name='foo'
with these conditions:
if approve is True, then return that one (only one will be true for the same name)
otherwise select the one that has highest score
I was looking into IF...ELSE but cannot even come up with a query that executes (despite a working one...)
How to set up the query command for this type of queries?
In SQL, you can often use some logic by defining the right order and limit:
select id
from my_table
where name = 'foo'
order by approve desc, score desc
limit 1
I have a table that looks like this:
control=# select * from animals;
age_range | weight | species
-----------+--------+---------
0-9 | 1 | lion
0-9 | 2 | lion
10-19 | 2 | tiger
10-19 | 3 | horse
20-29 | 2 | tiger
20-29 | 2 | zebra
I perform a query that summarizes weights of animals within age range groups, and I only want to return rows that have aggregated weights above
a certain number.
Summary Query:
SELECT
age_range,
SUM(animals.weight) AS weight,
COUNT(DISTINCT animals.species) AS distinct_species
FROM animals
GROUP BY age_range
HAVING SUM(animals.weight) > 3;
Summary Results:
age_range | weight | distinct_species
-----------+--------+------------------
10-19 | 5 | 2
20-29 | 4 | 2
Now here's the rub. Along with this summary, I want to report the distinct number of species used to create the above summary row set as a whole. For simplicity, let's refer to this number as the 'Distinct Species Total'. In this simple example, since only 3 species (tiger, zebra, horse) were used in yielding the 2 rows of this summary, and not 'lion', the 'Distinct Species Total' should be 3. But I can't figure out how to successfully query for that number. Since the summary query must use a having clause in order to apply a filter to an already grouped and aggregated row set, this presents problems in trying to query for the 'Distinct Species Total'.
This returns the wrong number, 2, because it is incorrectly a distinct count of a distinct count:
SELECT
COUNT(DISTINCT distinct_species) AS distinct_species_total
FROM (
SELECT
age_range,
SUM(animals.weight) AS weight,
COUNT(DISTINCT animals.species) AS distinct_species
FROM animals
GROUP BY age_range
HAVING SUM(animals.weight) > 3
) x;
And of course this returns the wrong number, 4, because it does not consider filtering the grouped and aggregated summary result using a having clause:
SELECT
COUNT(DISTINCT species) AS distinct_species_total
FROM animals;
Any help at all in getting leading me on the right path here is appreciated, and will hopefully help others with a similar problem, but in the end I do need a solution that will work with Amazon Redshift.
Join the result set with the original animals table and count the distinct species.
select distinct x.age_range,x.weight,count(distinct y.species) as distinct_species_total
from
(
select age_range,sum(animals.weight) as weight
from animals
group by age_range
having sum(animals.weight) > 3
) x
join animals y on x.age_range=y.age_range
Let's say I have this 3 tables
Countries ProvOrStates MajorCities
-----+------------- -----+----------- -----+-------------
Id | CountryName Id | CId | Name Id | POSId | Name
-----+------------- -----+----------- -----+-------------
1 | USA 1 | 1 | NY 1 | 1 | NYC
How do you get something like
---------------------------------------------
CountryName | ProvinceOrState | MajorCities
| (Count) | (Count)
---------------------------------------------
USA | 50 | 200
---------------------------------------------
Canada | 10 | 57
So far, the way I see it:
Run the first SELECT COUNT (GROUP BY Countries.Id) on Countries JOIN ProvOrStates,
store the result in a table variable,
Run the second SELECT COUNT (GROUP BY Countries.Id) on ProvOrStates JOIN MajorCities,
Update the table variable based on the Countries.Id
Join the table variable with Countries table ON Countries.Id = Id of the table variable.
Is there a possibility to run just one query instead of multiple intermediary queries? I don't know if it's even feasible as I've tried with no luck.
Thanks for helping
Use sub query or derived tables and views
Basically If You You Have 3 Tables
select * from [TableOne] as T1
join
(
select T2.Column, T3.Column
from [TableTwo] as T2
join [TableThree] as T3
on T2.CondtionColumn = T3.CondtionColumn
) AS DerivedTable
on T1.DepName = DerivedTable.DepName
And when you are 100% percent sure it's working you can create a view that contains your three tables join and call it when ever you want
PS: in case of any identical column names or when you get this message
"The column 'ColumnName' was specified multiple times for 'Table'. "
You can use alias to solve this problem
This answer comes from #lotzInSpace.
SELECT ct.[CountryName], COUNT(DISTINCT p.[Id]), COUNT(DISTINCT c.[Id])
FROM dbo.[Countries] ct
LEFT JOIN dbo.[Provinces] p
ON ct.[Id] = p.[CountryId]
LEFT JOIN dbo.[Cities] c
ON p.[Id] = c.[ProvinceId]
GROUP BY ct.[CountryName]
It's working. I'm using LEFT JOIN instead of INNER JOIN because, if a country doesn't have provinces, or a province doesn't have cities, then that country or province doesn't display.
Thanks again #lotzInSpace.
I want to return unique items based on condition, sorted by price asc. My query fails because Postgres wants items.id to be present in the group by clause. If it's included the query returns everything matching the where clause, which is not what I want. Why do I need to include the column?
select items.*
from items
where product_id = 1 and items.status = 'in_stock'
group by condition /* , items.id returns everything */
order by items.price asc
| id | condition | price |
--------------------------
| 1 | new | 9 |
| 2 | good | 5 |
| 3 | good | 3 |
I only want items with ids 1 and 3.
Update: Here's a fiddle using the answer below, which still produces the error:
http://sqlfiddle.com/#!1/33786/2
The problem is that PostgreSQL has no way of knowing which items records you want to take values from; that is, it can't tell that you want this:
| id | condition | price |
--------------------------
| 1 | new | 9 |
| 3 | good | 3 |
and not this:
| id | condition | price |
--------------------------
| 1 | new | 9 |
| 2 | good | 5 |
To fix this, you need to use some sort of aggregation function, such as MAX:
SELECT MAX(id) AS id,
condition,
MAX(price) AS price
FROM items
WHERE product_id = 1
AND status = 'in_stock'
GROUP BY condition
ORDER BY price ASC
which gives:
| id | condition | price |
--------------------------
| 1 | new | 9 |
| 3 | good | 5 |
(This restriction is part of the SQL standard, and most DBMSes enforce it. One exception is MySQL, which allows your query, but with the caveat that "The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate" [link].)
SQL Fiddle
select *
from (
select distinct on (cond)
id, cond, price
from items
where product_id = 1 and items.status = 'in_stock'
order by cond, price
) s
order by price
The SQL standard requires this behaviour, though some databases like MySQL ignore it and instead return unpredictable results.
If there's more than one row for "cond = good" and you ask for the "id" of the row where "cond = good", which row should the database give you? The row with id = 3, or id = 2? How should it know which to pick? MySQL picks an arbitrary row if there are multiple candidates, but this isn't allowed by the standard.
In your case you seem to want to pick the lowest-price row for each condition.
PostgreSQL provides an extension, DISTINCT ON ..., to help with this. Clodaldo has demonstrated this in his answer, so I won't repeat that here. Using DISTINCT ON will be much more efficient than the example below.
The SQL-standard way would be to use a window to rank the results, then filter on the ranked data. Unfortunately this is pretty inefficient as it requires all rows that match the inner where clause to be collected and sorted.
SELECT *
FROM (
SELECT *, dense_rank() OVER w AS itemrank
FROM items
WHERE product_id = 1 AND items.status = 'in_stock'
WINDOW w AS (PARTITION BY cond ORDER BY price ASC)
) ranked_items
WHERE itemrank = 1;
(http://sqlfiddle.com/#!1/33786/19)
Another SQL-standard way is to use an aggregation subquery to find the min prices for each category then display all rows with the min price:
SELECT *
FROM items INNER JOIN (
SELECT cond, min(price) AS minprice
FROM items
WHERE product_id = 1 AND items.status = 'in_stock'
GROUP BY cond
) minprices(cond, price)
ON (items.price = minprices.price AND items.cond = minprices.cond)
ORDER BY items.price;
Unlike the DISTINCT ON version, though, this will display multiple entries if the lowest priced item has more than one entry with the same cond and price.
So.. you should really use the DISTINCT ON approach, but you need to understand it. Start with the PostgreSQL documentation here.
On a side note, newer PostgreSQL versions allow you to refer to any column of a table whose primary key you've listed in GROUP BY; they identify the functional dependency of the other columns on the primary key. So you don't have to aggregate other cols if you've mentioned the PK in newer versions. That's what the standard requires, but older versions weren't smart enough to figure it out and required all columns to be listed explicitly.
That's what people who ask this question usually want to know, but doesn't apply strictly to your question since it turns out you're trying to use GROUP BY to filter rows.