I have two tables where one table represent the survey with the location and the other table the people interviewed (there are many people for each survey). I'm trying to show the count of people over a certain age in each location, however some provinces don't have anyone over certain ages therefore don't show in the resulting table. I would like the count to show zero if no one is over a certain age.
I have:
SELECT a.location, Count([b.age])
FROM Survey AS a LEFT JOIN person AS b ON a.surveyid = b.surveyid
Where b.age >= 85
GROUP BY a.location;
I realize that the WHERE clause is what is eliminating the zero count results but I can't figure out the subquery I would need.
Use conditional aggregation instead. That means moving the boolean condition to the argument of the aggregation function
SELECT s.location,
SUM(IIF(p.age >= 85, 1, 0))
FROM Survey AS s LEFT JOIN
person AS p
ON s.surveyid = p.surveyid
GROUP BY s.location;
Noticed that I changed the table aliases to be abbreviations of the table names. This makes the query easier to follow.
Related
I have 2 tables. One lists all the goals scored in the English Premier League and who scored it and the other, the squad numbers of each player in the league.
I want to do a join so that the table sums the total number of goals by player name, and then looks up the squad number of that player.
Table A [goal_scorer]
[]1
Table B [squads]
[]2
I have the SQL query below:
SELECT goal_scorer.*,sum(goal_scorer.number),squads.squad_number
FROM goal_scorer
Inner join squads on goal_scorer.name=squads.player
group by goal_scorer.name
The issue I have is that in the result, the sum of 'number' is too high and seems to include duplicate rows. For example, Aaron Lennon has scored 33 times, not 264 as shown below.
Maybe you want something like this?
SELECT goal_scorer.*, s.total, squads.squad_number
FROM goal_scorer
LEFT JOIN (
SELECT name, sum(number) as total
FROM goal_scorer
GROUP BY name
) s on s.name = goal_scorer.name
JOIN squads on goal_scorer.name=squads.player
There are other ways to do it, but here I'm using a sub-query to get the total by player. NB: Most modern SQL platforms support windowing functions to do this too.
Also, probably don't need the left on the sub-query (since we know there will always be at least one name), but I put it in case your actual use case is more complicated.
Can you try this if you are using sql-server?
select *
from squads
outer apply(
selecr sum(goal_scorer.number) as score
from goal_scorer where goal_scorer.name=squads.player
)x
What my issue is:
I am constantly returning multiple values when I don't expect to. I am attempting to get a specific climate, determined by the state, county, and country.
What I've tried:
The code given below. I am unsure as to what is wrong with it specifically. I do know that it is returning multiple values. But why? I specify that STATE_ABBREVIATION = PROV_TERR_STATE_LOC and with the inner joins that I do, shouldn't that create rows that are similar except for their different CLIMATE_IDs?
SELECT
...<code>...
(SELECT locations.CLIMATE_ID
FROM REF_CLIMATE_LOCATION locations, SED_BANK_TST.dbo.STATIONS stations
INNER JOIN REF_STATE states ON STATE_ID = states.STATE_ID
INNER JOIN REF_COUNTY counties ON COUNTY_ID = counties.COUNTY_ID
INNER JOIN REF_COUNTRY countries ON COUNTRY_ID = countries.COUNTRY_ID
WHERE STATE_ABBREVIATION = PROV_TERR_STATE_LOC) AS CLIMATE_ID
...<more code>...
FROM SED_BANK_TST.dbo.STATIONS stations
I've been at this for hours, looking up different questions on SO, but I cannot figure out how to make this subquery return a single value.
All those inner joins don't reduce the result set if the IDs you're testing exist in the REF tables. Apart from that you're doing a Cartesian product between locations and stations (which may be an old fashioned inner join because of the where clause).
You'll only get a single row if you only have a single row in the locations table that matches a single row in the stations table under the condition that STATE_ABBREVIATION = PROV_TERR_STATE_LOC
Your JOINs show a hierarchy of locations: Country->State->County, but your WHERE clause only limits by the state abbreviation. By joining the county you'll get one record for every county in that state. You CAN limit your results by taking the TOP 1 of the results, but you need to be very careful that that's really what you want. If you're looking for a specific county, you'll need to include that in the WHERE clause. You get some control with the TOP 1 in that it will give the top 1 based on an ORDER BY clause. I.e., if you want the most recently added, use:
SELECT TOP 1 [whatever] ORDER BY [DateCreated] DESC;
For your subquery, you can do something like this:
SELECT TOP 1
locations.CLIMATE_ID
FROM REF_CLIMATE_LOCATION locations ,
SED_BANK_TST.dbo.STATIONS stations
INNER JOIN REF_STATE states ON STATE_ID = states.STATE_ID
INNER JOIN REF_COUNTY counties ON COUNTY_ID = counties.COUNTY_ID
INNER JOIN REF_COUNTRY countries ON COUNTRY_ID = countries.COUNTRY_ID
WHERE STATE_ABBREVIATION = PROV_TERR_STATE_LOC
Just be sure to either add an ORDER BY at the end or be okay with it choosing the TOP 1 based on the "natural order" on the tables.
If you are expecting to have a single value on your sub-query, probably you need to use DISTINCT. The best way to see it is you run your sub-query separately and see the result. If you need to include other columns from the tables you used, you may do so to check what makes your result have multiple rows.
You can also use MAX() or MIN() or TOP 1 to get a single value on the sub-query but this is dependent to the logic you want to achieve for locations.CLIMATE_ID. You need to answer the question, "How is it related to the rest of the columns retrieved?"
Given the schema here I'm trying to understand and solve the below 3 sql queries as I'm confused:
1- Present a table giving the names of the countries with ≥ 50% urbanization
rates, their urbanization rates, and their per capita GDP. Note that
urbanization rate is the percentage of population living in cities. Do not
count cities with NULL values for population.
SELECT country.name, round(sum(city.population)/country.population, 3) AS urban, round(gdp/country.population, 3) AS gdppc
FROM city
INNER JOIN country ON code = country
INNER JOIN economy ON code = economy.country
WHERE city.population IS NOT NULL
GROUP BY country.name, country.population, economy.gdp
HAVING round(sum(city.population)/country.population, 3) >= 0.5
ORDER BY urban DESC;
In the above query, Why I need to include country.population and economy.gdp in the GROUP BY? If I tried using just country.name in the GROUP BY I get an error saying I should include the others.
2- Show organizations that have as members all the European countries with over 50 million people?
SELECT name
FROM organization
INNER JOIN (SELECT organization
FROM country
INNER JOIN encompasses
ON code = encompasses.country
INNER JOIN ismember
ON code = ismember.country
WHERE population > 50000000 AND continent = 'Europe'
GROUP BY organization
HAVING count(ismember.country) = (SELECT count(*)
FROM country
INNER JOIN encompasses
ON code = country
WHERE population > 50000000 AND continent = 'Europe'))
AS innerQuery
ON abbreviation = innerQuery.organization;
Why I need the HAVING Part above?
3- Insert a new organization called “Tivoli” and a trigger that says if Germany joins “Tivoli” then so too must the UK and France. Insert Germany into the “Tivoli” organization. Confirm proper behavior.
I tried the below script but it's not working, any advice please?
do $$
begin
IF(NOT EXISTS ( SELECT 1 FROM organization WHERE organization."name" = 'Tivoli' AND organization.country = 'D' ))
BEGIN
INSERT INTO organization VALUES ('Tivoli','Tivoli organization',NULL,'F',NULL,NULL);
INSERT INTO organization VALUES ('Tivoli','Tivoli organization',NULL,'GB',NULL,NULL);
END;
end $$
1)
You used country.population and economy.gdp in the select, outside of aggregate functions ( COUNT(), AVG() and SUM() ), and you have a GROUP BY. Everything that you select has to be in GROUP BY or inside of aggregate functions.
2)
Because you were asked to show organizations that have ALL of 50mil + people countries. With HAVING, you check if that organization has the right amount of countries.
3)
organization."name" = 'Tivoli'
It's supposed to be :
organization.name
First of all, you should limit a question to one only, not 3. But here are some pointers for all 3:
In the above query, Why I need to include country.population and economy.gdp in the GROUP BY? If I tried using just country.name in the GROUP BY I get an error saying I should include the others.
This is a requirement. A group by country.name alone would work (in Postgres 9.1+) only if the other two fields are known to be functionally dependent on country.name. But probably country.name is not the primary key of the country table, so in theory it is possible to have two records in that table with the same name, but different population.
The rule is as follows:
When GROUP BY is present, it is not valid for the SELECT list expressions to refer to ungrouped columns except within aggregate functions or if the ungrouped column is functionally dependent on the grouped columns, since there would otherwise be more than one possible value to return for an ungrouped column. A functional dependency exists if the grouped columns (or a subset thereof) are the primary key of the table containing the ungrouped column.
This is implemented since version 9.1.
Why I need the HAVING Part above?
Because a condition on an aggregate (count in this case) can only be performed after grouping, and can thus not be expressed in the where clause. In this case the having clause makes sure that the organisation is not only present in some big EU Member States, but all big EU Member states.
I tried the below script but it's not working, any advice please?
Without a proper database schema, it is not possible to provide you with the correct SQ, but from the ERD diagram it seems that the organization table does not have a country field. Instead the ismember table connects organizations with countries. You would only insert one organization, but several ismember records (one per Member State involved)
It is better also to name the fields in your insert statement, so it is clear which value corresponds to which field.
I have a table called Apartments that has three columns: apartment_type, person, date. It includes the apartment type selected by a certain person and date. I need to count how many people picked each of the apartment types. Some apartment type have 0 population.
Here is my query:
SELECT apartment_type, COUNT(*) AS TOTAL
FROM Apartments
GROUP BY apartment_type
It works great, but it doesn't include apartment types with a value of 0. Please, help me to correct this query.
In case some appartment_type have 0 population - your table will not contain any record with that type - so you must add some join from another table, where all apartment types exists. Or use union to create all 0 populated entries.
Something like:
SELECT apartment_type, COUNT(*) AS TOTAL
FROM (SELECT * FROM Apartments UNION ALL SELECT apartment_type, 0 as person, 0 as date from SomeTableWithFullListOfTypes group by apartment_type) as tmp
GROUP BY apartment_type
I generally agree with Nosyara's answer, but I don't agree with his sample query with the union all. I'm not sure it works, and it's certainly too complicated.
As stated already, if you don't have a table with all the possible apartment types, create one. Then you can write your query using a simple left join:
select t.apartment_type, count(a.apartment_type) as total
from apartment_types t
left join apartments a
on a.apartment_type = t.apartment_type
group by t.apartment_type
Note how count(*) was replaced by count(a.apartment_type). That change is necessary to have an accurate count in the case where you don't have apartments for a certain apartment type.
SELECT apartment_type, COUNT(apartment.*) AS TOTAL
FROM apartment_type
left join apartment
on apartment_type.aparentment_type = apartements.apartment_type
GROUP BY apartment_type
Using a left join will give you everything from the left side of the join (so all your types) and anything from the right that matches.
I want to retrieve the course_id in table course that is not in the table takes. Table takes only contains course_id of courses taken by students. The problem is that if I have:
select count (distinct course.course_id)
from course, takes
where course.course_id = (takes.course_id);
the result is 85 which is smaller than the total number of course_id in table course, which is 200. The result is correct.
But I want to find the number of course_id that are not in the table takes, and I have:
select count (distinct course.course_id)
from course, takes
where course.course_id != (takes.course_id);
The result is 200, which is equal the number of course_id in table course. What is wrong with my code?
This SQL will give you the count of course_id in table course that aren't in the table takes:
select count (*)
from course c
where not exists (select *
from takes t
where c.course_id = t.course_id);
You didn't specify your DBMS, however, this SQL is pretty standard so it should work in the popular DBMSs.
There are a few different ways to accomplish what you're looking for. My personal favorite is the LEFT JOIN condition. Let me walk you through it:
Fact One: You want to return a list of courses
Fact Two: You want to
filter that list to not include anything in the Takes table.
I'd go about this by first mentally selecting a list of courses:
SELECT c.Course_ID
FROM Course c
and then filtering out the ones I don't want. One way to do this is to use a LEFT JOIN to get all the rows from the first table, along with any that happen to match in the second table, and then filter out the rows that actually do match, like so:
SELECT c.Course_ID
FROM
Course c
LEFT JOIN -- note the syntax: 'comma joins' are a bad idea.
Takes t ON
c.Course_ID = t.Course_ID -- at this point, you have all courses
WHERE t.Course_ID IS NULL -- this phrase means that none of the matching records will be returned.
Another note: as mentioned above, comma joins should be avoided. Instead, use the syntax I demonstrated above (INNER JOIN or LEFT JOIN, followed by the table name and an ON condition).