Quick question... I have a query that checks for duplicates that looks like this:
SELECT COUNT( * ) AS repetitions, Name, Phone, ID, categoryid, State
FROM users
GROUP BY Name, Phone, State
HAVING repetitions > 1
ORDER BY ID DESC
this works but MySQL returns the first ID in a set of duplicates. For example, lets say I have 2 rows. ID for row one is 1 and ID for row two is 2 and Name, Phone and State have identical data... How can i get the above query to return the count but with the ID "2" instead of "1"?
Thanks! ;)
Use the max() aggregate function:
SELECT COUNT(*) AS repetitions, max(ID) FROM users GROUP BY Name, Phone, State HAVING repetitions > 1 ORDER BY ID DESC
not perfect but works
SELECT COUNT( * ) AS repetitions, Name, Phone, MAX(ID), categoryid, State
FROM users
GROUP BY Name, Phone, State
HAVING repetitions > 1
Related
I'm using sqlite3, I have the following table:
"who" stands for the id of users. say who with id "4" stands for "John". John made 7 purchases. I would like to have a select query that sums all the shares of John. so the select query on shares based on who of "4" returns 113. how can I do that?
You want a where clause and a sum():
select sum(shares) as total_shares
from mytable
where who = 4
Or if you want the result for all users at once, with each user on a separate row:
select who, sum(shares) as total_shares
from mytable
group by who
You can also count how many records each user has if you like:
select who, sum(shares) as total_shares, count(*) as cnt
from mytable
group by who
Given the following table where the Name value might be repeated in multiple rows:
How can we determine how many times a Name value exists in the table and can we filter on names that have a specific number of occurrances.
For instance, how can I filter this table to show only names that appear twice?
You can use group by and having to exhibit names that appear twice in the table:
select name, count(*) cnt
from mytable
group by name
having count(*) = 2
Then if you want the overall count of names that appear twice, you can add another level of aggregation:
select count(*) cnt
from (
select name
from mytable
group by name
having count(*) = 2
) t
It sounds like you're looking for a histogram of the frequency of name counts. Something like this
with counts_cte(name, cnt) as (
select name, count(*)
from mytable
group by name)
select cnt, count(*) num_names
from counts_cte
group by cnt
order by 2 desc;
You need to use a GROUP BY clause to find counts of name repeated as
select name, count(*) AS Repeated
from Your_Table_Name
group by name;
If You want to show only those Which are repeated more than one times. Then use the below query which will show those occurrences which are there more than one times.
select name, count(*) AS Repeated
from Your_Table_Name
group by name having count(*) > 1;
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
)
I have a table Student in SQL Server with these columns:
[ID], [Age], [Level]
I want the query that returns each age value that appears in Students, and finds the level value that appears most often. For example, if there are more 'a' level students aged 18 than 'b' or 'c' it should print the pair (18, a).
I am new to SQL Server and I want a simple answer with nested query.
You can do this using window functions:
select t.*
from (select age, level, count(*) as cnt,
row_number() over (partition by age order by count(*) desc) as seqnum
from student s
group by age, level
) t
where seqnum = 1;
The inner query aggregates the data to count the number of levels for each age. The row_number() enumerates these for each age (the partition by with the largest first). The where clause then chooses the highest values.
In the case of ties, this returns just one of the values. If you want all of them, use rank() instead of row_number().
One more option with ROW_NUMBER ranking function in the ORDER BY clause. WITH TIES used when you want to return two or more rows that tie for last place in the limited results set.
SELECT TOP 1 WITH TIES age, level
FROM dbo.Student
GROUP BY age, level
ORDER BY ROW_NUMBER() OVER(PARTITION BY age ORDER BY COUNT(*) DESC)
Or the second version of the query using amount each pair of age and level, and max values of count pair age and level per age.
SELECT *
FROM (
SELECT age, level, COUNT(*) AS cnt,
MAX(COUNT(*)) OVER(PARTITION BY age) AS mCnt
FROM dbo.Student
GROUP BY age, level
)x
WHERE x.cnt = x.mCnt
Demo on SQLFiddle
Another option but will require later version of sql-server:
;WITH x AS
(
SELECT age,
level,
occurrences = COUNT(*)
FROM Student
GROUP BY age,
level
)
SELECT *
FROM x x
WHERE EXISTS (
SELECT *
FROM x y
WHERE x.occurrences > y.occurrences
)
I realise it doesn't quite answer the question as it only returns the age/level combinations where there are more than one level for the age.
Maybe someone can help to amend it so it includes the single level ages aswell in the result set: http://sqlfiddle.com/#!3/d597b/9
with combinations as (
select age, level, count(*) occurrences
from Student
group by age, level
)
select age, level
from combinations c
where occurrences = (select max(occurrences)
from combinations
where age = c.age)
This finds every age and level combination in the Students table and counts the number of occurrences of each level.
Then, for each age/level combination, find the one whose occurrences are the highest for that age/level combination. Return the age and level for that row.
This has the advantage of not being tied to SQL Server - it's vanilla SQL. However, a window function like Gordon pointed out may perform better on SQL Server.
Let's say I have the following query.
SELECT ID, Email, ProductName, ProductModel FROM Products
How can I modify it so that it returns no duplicate Emails?
In other words, when several rows contain the same email, I want the results to include only one of those rows (preferably the last one). Duplicates in other columns should be allowed.
Clauses like DISTINCT and GROUP BY appear to work on entire rows. So I'm not sure how to approach this.
If you are using SQL Server 2005 or above use this:
SELECT *
FROM (
SELECT ID,
Email,
ProductName,
ProductModel,
ROW_NUMBER() OVER(PARTITION BY Email ORDER BY ID DESC) rn
FROM Products
) a
WHERE rn = 1
EDIT:
Example using a where clause:
SELECT *
FROM (
SELECT ID,
Email,
ProductName,
ProductModel,
ROW_NUMBER() OVER(PARTITION BY Email ORDER BY ID DESC) rn
FROM Products
WHERE ProductModel = 2
AND ProductName LIKE 'CYBER%'
) a
WHERE rn = 1
This assumes SQL Server 2005+ and your definition of "last" is the max PK for a given email
WITH CTE AS
(
SELECT ID,
Email,
ProductName,
ProductModel,
ROW_NUMBER() OVER (PARTITION BY Email ORDER BY ID DESC) AS RowNumber
FROM Products
)
SELECT ID,
Email,
ProductName,
ProductModel
FROM CTE
WHERE RowNumber = 1
When you use DISTINCT think of it as a distinct row, not column. It will return only rows where the columns do not match exactly the same.
SELECT DISTINCT ID, Email, ProductName, ProductModel
FROM Products
----------------------
1 | something#something.com | ProductName1 | ProductModel1
2 | something#something.com | ProductName1 | ProductModel1
The query would return both rows because the ID column is different. I'm assuming that the ID column is an IDENTITY column that is incrementing, if you want to return the last then I recommend something like this:
SELECT DISTINCT TOP 1 ID, Email, ProductName, ProductModel
FROM Products
ORDER BY ID DESC
The TOP 1 will return only the first record, by ordering it by the ID descending it will return the results with the last row first. This will give you the last record.
You can over that by using GROUP BY like this:
SELECT ID, Email, ProductName, ProductModel
FROM Products
GROUP BY Email
For Access, you can use the SQL Select query I present here:
For example you have this table:
CLIENTE|| NOMBRES || MAIL
888 || T800 ARNOLD || t800.arnold#cyberdyne.com
123 || JOHN CONNOR || s.connor#skynet.com
125 || SARAH CONNOR ||s.connor#skynet.com
And you need to select only distinct mails.
You can do it with this:
SQL SELECT:
SELECT MAX(p.CLIENTE) AS ID_CLIENTE
, (SELECT TOP 1 x.NOMBRES
FROM Rep_Pre_Ene_MUESTRA AS x
WHERE x.MAIL=p.MAIL
AND x.CLIENTE=(SELECT MAX(l.CLIENTE) FROM Rep_Pre_Ene_MUESTRA AS l WHERE x.MAIL=l.MAIL)) AS NOMBRE,
p.MAIL
FROM Rep_Pre_Ene_MUESTRA AS p
GROUP BY p.MAIL;
You can use this to select the maximum ID, the correspondent name to that maximum ID , you can add any other attribute that way. Then at the end you put the distinct column to filter and you only group it with that last distinct column.
This will bring you the maximum ID with the correspondent data, you can use min or any other functions and you replicate that function to the sub-queries.
This select will return:
CLIENTE|| NOMBRES || MAIL
888 || T800 ARNOLD || t800.arnold#cyberdyne.com
125 || SARAH CONNOR ||s.connor#skynet.com
Remember to index the columns you select and the distinct column must have not numeric data all in upper case or in lower case, or else it won't work.
This will work with only one registered mail as well.
Happy coding!!!
The reason DISTINCT and GROUP BY work on entire rows is that your query returns entire rows.
To help you understand: Try to write out by hand what the query should return and you will see that it is ambiguous what to put in the non-duplicated columns.
If you literally don't care what is in the other columns, don't return them. Returning a random row for each e-mail address seems a little useless to me.
Try This
;With Tab AS (SELECT DISTINCT Email FROM Products)
SELECT Email,ROW_NUMBER() OVER(ORDER BY Email ASC) AS Id FROM Tab
ORDER BY Email ASC
Try this:
SELECT ID, Email, ProductName, ProductModel FROM Products WHERE ID IN (SELECT MAX(ID) FROM Products GROUP BY Email)