I have the following data in my database table, since I'm fairly new to MYSQL i'm having problems in querying it to give me the following output
City Subject
london english
toronto math
london math
london math
toronto english
toronto english
There can only be two subjects, english or math. Im trying to output the data this way, first the query should pick all the distinct items in the city column. Then tell me the count of each subject in that city.
output
city English Math
london 1 2
toronto 2 1
I tried grouping, but since I don't know mysql that well, I realized it just groups the subjects together and eats the cities while grouping.
try this:
SELECT city,
SUM(IF(subject='english',1,0)) AS English,
SUM(IF(subject='math',1,0)) AS Math
FROM foo
GROUP BY city;
Related
I have a table named sales in a MySQL database that looks like this:
company manufactured shipped
Mercedes Germany United States
Mercedes Germany Germany
Mercedes Germany United States
Toyota Japan Canada
Toyota Japan England
Audi Germany United States
Audi Germany France
Audi Germany Canada
Tesla United States Mexico
Tesla United States Canada
Tesla United States United States
Here is a Fiddle: http://www.sqlfiddle.com/#!17/145ff/3
I would like to return the list of companies that ship ALL of their products internationally (that is, where the value in the manufactured column differs from the value in the shipped column for ALL records of a particular company).
Using the example above, the desired result set would be:
company
Toyota
Audi
Here is my (hackish) attempt:
WITH temp_table AS (
SELECT
s.company AS company
, SUM(CASE
WHEN s.manufactured != s.shipped THEN 1
ELSE 0
END
) AS count_international
, COUNT(s.company) AS total_within_company
FROM
sales s
GROUP BY
s.company
)
SELECT
company
FROM
temp_table
WHERE count_international = total_within_company
Essentially, I count the instances where the columns do not match. Then I check whether the sum of those mismatched instances matches the number of records within a given group.
This approach works, but it's far from an elegant solution!
Can anyone offer advice as to a more idiomatic way to implement this query?
Thanks!
We can GROUP BY company and use a HAVING clause to say all countries in shipped must differ to the country in manufactured:
SELECT company
FROM sales
GROUP BY company
HAVING COUNT(CASE WHEN manufactured = shipped THEN 1 END) = 0;
Try out here: db<>fiddle
The fiddle linked in the question is a Postgres DB, but MySQL is taged as DBMS.
In a MySQL DB, the above query can be simplified to:
SELECT company
FROM sales
GROUP BY company
HAVING SUM(manufactured = shipped) = 0;
In a Postgres DB, this is not possible.
You have to think in sets... you want to display all without a match -- find the matches display the rest
SELECT DISTINCT company
FROM sales
WHERE company NOT IN (
SELECT company
FROM sales
WHERE manufactured = shipped
)
I want to fetch records from a table that contains duplicate records. I want the output to be like only two duplicate records from each set of duplicate records in overall record output set.
example-
Name
Country
John
India
Mark
India
Chris
Russia
Feggy
England
Rain
Russia
Monesy
Russia
Bhumi
India
Peter
England
Bruice
England
Radhe
India
Output should have only two duplicate set of records from all duplicate of similar type as we can see in output below the country is repeating only two times and it took only first two counters of duplicate records in final record set -
Name
Country
John
India
Mark
India
Chris
Russia
Feggy
England
Rain
Russia
Peter
England
You can number the lines by the window and select only the first N.
Sorting should be chosen according to the business logic of the query.
For example:
;WITH numbered_name AS
(
SELECT *
, ROW_NUMBER() OVER (PARTITION BY t.Country ORDER BY t.Name) rn
FROM table t
)
SELECT Name
, Country
FROM numbered_name
WHERE rn <= 2
Name Place visited
Ash New york
Bob New york
Ash Chicago
Bob Chicago
Carl Chicago
Carl Detroit
Dan Detroit
Above is the sample table. The output should be two names who visited place together. I.e. the output should be Ash and Bob since the places visited by Ash also visited by Bob.
Output:
Name1 Name2
Ash Bob
What is a query for this using MySQL or even relational algebra?
The simplest method is to use group_concat(). Assuming no duplicates,
select places, group_concat(names) as names
from (select name, group_concat(place order by place) as places
from t
group by name
) t
group by places
having count(*) > 1;
This will return all the names with exactly the same places on a single row. The names will be in a comma-delimited list.
This question already has an answer here:
How to output table results by using cfoutput group by date?
(1 answer)
Closed 7 years ago.
I'm working on outputting values from data base in the table. My table has 5 columns: Date, FirstName, LastName, City, State. Here is example of my data base table:
DateMeeting FirstName LastName City State
2015-12-11 Mike Johns Dallas TX
2015-12-11 John Cook Dallas TX
2015-12-11 Nick Roberts Dallas TX
2015-12-11 Oliver Ryan New York NY
2015-12-11 Michael Best New York NY
2015-12-11 David Holmes New York NY
So I want to have output table that will display just one date for multiple records. I tried to use DISTINCT on the date and that works fine but if I include my WHERE clause for City and State my query breaks. Also I tried to use GROUP BY but same problem, I can get Date values only once as long as I do not include other columns. In this case I need all columns but my Date value only once. Here is my query that I use:
Select Distinct(DateMeeting),FirstName, LastName, City, State
From Customers
Where City = 'Dallas'
and State = 'TX'
This query does not work with all columns that I have in my select, only if I run DISTINCT(DateMeeting). I would like to output my values in the table to look like this:
Date First Name Last Name City State
Mike Johns Dallas TX
John Cook Dallas TX
Nick Roberts Dallas TX
2015-12-11 Oliver Ryan New York NY
Michael Best New York NY
David Holmes New York NY
If anyone knows how this can be done please let me know. Thank you.
Each layer in the technology stack has its strengths and weaknesses.
As for mysql, do not turn it into a report engine as described with blank date columns except for one per date somewhere in the middle of a date chunk as shown. Subsequent dates as ordered will get muddled and confused.
True, one could use slightly interesting mysql variables and dump it just on the first row of a chunk. But for what.
Play to mysql's strengths, return all the data. And have the front-end (coldfusion or whatever), deal with the reporting features you desire for the output.
id points year country
-----------------------------------
1 45 1998 Mexico
2 45 2000 Germany
3 47 2010 Russia
4 45 1970 China
5 49 2010 Austria
I wonder how can I take row results considering only 2 items from country column. For example only records where country is Germany and Mexico. When I try to get results where only 1 country is criterion the thing is easy:
SELECT * FROM List WHERE Country='Mexico';
the result is:
id points year country
-----------------------------------
1 45 1998 Mexico
but when I try to get results where 2 country items are criteria problems start. I tried:
SELECT * FROM List WHERE country='Mexico' AND Country='Germany';
SELECT * FROM List WHERE country='Mexico' AND 'Germany';
SELECT * FROM List WHERE country='Mexico','Germany';
SELECT * FROM List WHERE country='Mexico'AND WHERE country='Germany';
but no desired result:
id points year country
-----------------------------------
1 45 1998 Mexico
2 45 2000 Germany
I understand that maybe I committed logical error because there is no single record where country is Mexico and Germany at same time, and sql maybe understands claim exactly that way, but, how to write correctly in sql language: Give me results for records where countries are Mexico and Germany. Thanks.
You are looking for IN operator
SELECT * FROM List WHERE Country in ('Mexico','Germany');
Just use OR.
So instead of
SELECT * FROM List WHERE country='Mexico' AND Country='Germany';
it would be
SELECT * FROM List WHERE country='Mexico' OR country='Germany';
IN is also a good function to use, especially if you've got multiple values that you want to check against but that's been covered in the other answers.
You need to use or or in, you have been using and and asking mysql to find a row where country is both Mexico and Germany which is not true.
SELECT * FROM List WHERE Country in ('Mexico','Germany');
try this:
SELECT * FROM List WHERE country='Mexico' OR Country='Germany';
SQL is using logic. Natural language is not.
When you say that you want the results for a list of countries you need to specify so. This request corresponds to an logical or. Since the name can be one or the other, both are correct.
SELECT * FROM List WHERE Country = 'Mexico' OR Country = 'Germany'
To prevent further mistakes like these, I recommend that you look up logical operations in the docs (they are very good). MySQL or the PostGres, both should be fine.