Been doing a lot of searching and haven't really found an answer to my MYSQL issue.
SELECT DISTINCT name, type, state, country FROM table
Results in 1,795 records
SELECT DISTINCT name FROM table
Results in 1,504 records
For each duplicate "name"... "type", "state", "country" aren't matching in each record.
Trying to figure out how to SELECT the associated row to the DISTINCT name, without checking them for being DISTINCT or not
SELECT name, type, state, country FROM table GROUP BY name;
should do the trick.
If you want distinct name, you must decide which of the multiple values that may occur for each distinct name you want. For example, you may want minimals, or counts:
SELECT name, min(type), min(state), count(country) FROM table GROUP BY name
Related
I am filtering to a second created table that have duplicates removed. However I'm finding that DISTINCT seems not be working, and I end up with rows with identical ids. I want to only select one unique ID and throw any remaining ones away, but this is not what is happening. In other-words I do not care about the other column names.
def de_dupe_affiliates(read_table, write_table):
query = """
CREATE OR REPLACE TABLE `{write_table}` AS
SELECT DISTINCT ID, BRAND, TITLE, SHORT_TITLE, PRICE, FROM `{read_table}`
""".format(read_table=read_table,write_table=write_table)
response = client.query(query).result()
I also tried
SELECT DISTINCT(ID), BRAND
But this did the same. Is it possible to do this with a DISTINCT on one column?
Consider below approach
SELECT AS VALUE ANY_VALUE(t) FROM (
SELECT ID, BRAND, TITLE, SHORT_TITLE, PRICE FROM read_table
) t
GROUP BY ID
Your select clause
SELECT DISTINCT ID, BRAND, TITLE, SHORT_TITLE, PRICE FROM `{read_table}`
is equivalent to
SELECT ID, BRAND, TITLE, SHORT_TITLE, PRICE FROM `{read_table}` GROUP BY ID, BRAND, TITLE, SHORT_TITLE, PRICE
meaning any differences within these fields creates new rows in your result.
Your query works only if ID, BRAND, TITLE, SHORT_TITLE, PRICE fields are unique.
If not, you may use window functions like row_number() or rank() to select one row per id.
I have a problem with the following task from the platform Codesignal:
After some investigation, you've created a database containing a foreignCompetitors table, which has the following structure:
competitor: the name of the competitor;
country: the country in which the competitor is operating.
In your report, you need to include the number of competitors per country and an additional row at the bottom that contains a summary: ("Total:", total_number_of_competitors)
Given the foreignCompetitors table, compose the resulting table with two columns: country and competitors. The first column should contain the country name, and the second column should contain the number of competitors in this country. The table should be sorted by the country names in ascending order. In addition, it should have an extra row at the bottom with the summary, as described above.
Example
For the following table foreignCompetitors
my solution:
CREATE PROCEDURE solution()
BEGIN
(SELECT country, COUNT(*) AS competitors
FROM foreignCompetitors
GROUP BY country
ORDER BY country)
UNION
SELECT 'Total:', COUNT(*) FROM foreignCompetitors;
END
But my output is:
The result of the countries is not sorted by their names.
I cannot understand why is that even though I try to sort them with ORDER BY.
You want a GROUP BY WITH ROLLUP here:
SELECT COALESCE(country, 'Total:') AS country, COUNT(*) AS competitors
FROM foreignCompetitors
GROUP BY country WITH ROLLUP
ORDER BY country;
If you want to stick with your union approach, then you need to introduce a computed column into the union query which places the total row at the bottom of the result set. Consider:
SELECT country, competitors
FROM
(
SELECT country, COUNT(*) AS competitors, 1 AS pos
FROM foreignCompetitors
GROUP BY country
UNION ALL
SELECT 'Total:', COUNT(*), 2
FROM foreignCompetitors
) t
ORDER BY pos, country;
I have read in various websites about the count() function but I still cannot make this work.
I made a small table with (id, name, last name, age) and I need to retrieve all columns plus a new one. In this new column I want to display how many times a name shows up or repeats itself in the table.
I have made test and can retrieve but only COLUMN NAME with the count column, but I haven't been able to retrieve all data from the table.
Currently I have this
select a.n_showsup, p.*
from [test1].[dbo].[person] p,
(select count(*) n_showsup
from [test1].[dbo].[person])a
This gives me all data on output but on the column n_showsup it gives me just the number of rows, now I know this is because I'm missing a GROUP BY but then when I write group by NAME it shows me a lot of records. This is an example of what I need:
You can use window functions, if you RDBMS supports them:
select t.*, count(*) over(partition by name) n_showsup
from mytable t
Alternatively, you can join the table with an aggregation query that counts the number of occurences of each name:
select t.*, x.n_showsup
from mytable t
inner join (select name, count(*) n_showsup from mytable group by name) x
on x.name = t.name
While the window function approach (#GMB's answer) is the right way to go, thinking through this from a subquery approach (like you were headed towards) would look something like:
select p.*, a.n_showsup
from [test1].[dbo].[person] p
INNER JOIN (
select name, count(*) n_showsup
from [test1].[dbo].[person]
GROUP BY name
) a ON p.name = a.name
This is VERY close to what you had, the difference is that we are grouping that subquery by name (so we get a count by name) and we can use that in the join criteria which we do with the ON clause on that INNER JOIN.
You should really never ever use a comma in your FROM clause. Instead use a JOIN.
I need to show the ID (which is unique in every case) and the name, which is sometimes different. In my code I only want to show the names IF they are unique.
I tried with both distinct and count(*)=1, nothing solves my problem.
SELECT DISTINCT id, name
FROM person
GROUP BY id, name
HAVING count(name) = 1;
The result is still showing the names multiple times
By "unique", I assume you mean names that only appear once. That is not what "distinct" means in SQL; the use of distinct is to remove duplicates (either for counting or in a result set).
If so:
SELECT MAX(id), name
FROM person
GROUP BY name
HAVING COUNT(*) = 1;
If your DBMS supports it, you can use a window function:
SELECT id, name
FROM (
SELECT id, name, COUNT(*) OVER(PARTITION BY name) AS NameCount -- get count of each name
FROM person
) src
WHERE NameCount = 1
If not, you can do:
SELECT id, name
FROM person
WHERE name IN (
SELECT name
FROM person
GROUP BY name
HAVING COUNT(*) = 1 -- Only get names that occur once
)
Do I need to put all the column names in group by which I have select put in select?
for example in this simple query :
Select
CustomerID,
CompanyName,
ContactName,
ContactTitle,
City,
Country
From
Customers
Group By
Country,
CompanyName,
ContactName,
ContactTitle,
City,
Country,
CustomerID
I have to allways call same amount Group By what i used in Select?
If you're just selecting columns and you want the returned records to discard the exact duplicate rows? Then there are 2 methods.
1) group by
2) distinct
Your query doesn't use any of the aggregate functions like f.e. COUNT, MIN, MAX, SUM, ...
So your query could use DISTINCT instead of a GROUP BY.
select DISTINCT
CustomerID, CompanyName, ContactName, ContactTitle, City, Country
from Customers
But if CustomerID is a primary key, then CustomerID would already make the result unique.
So then this query doesn't need a GROUP BY or a DISTINCT to only get unique records.
select CustomerID, CompanyName, ContactName, ContactTitle, City, Country
from Customers
Note that one could have both DISTINCT and GROUP BY in the same query. But that's just pointless. A GROUP BY already enforces the uniqueness, so adding a DISTINCT to make them unique would just make the query slower for no reason.
As for the why all the columns in that select also have to be listed in the GROUP BY? Some databases, f.e. MySql can be more tolerant about not having to group on all columns. But it's a rule from one of the SQL Standards. So most databases enforce that. It's to avoid potential misleading results.
GROUP BY x, y means you want one result row per x and y. So if you have a table with bills, you could group by year and month for instance and thus get the number of bills (count(*)) and the total (sum(amount)) per month.
So the question is what rows do you want to see. A row per company (with the number of their customers) maybe? A row per city? The GROUP BY clause contains exactly those columns mentioned.
Your GROUP BY clause does exactly nothing, as select customers and you group by customer ID (which should be the customer table's primary key).