Sorry for the Title, But didn't know how to explain.
I have a table that have 2 fields A and B.
I want find all rows in the table that have duplicate A (more than one record) but at the same time A will consider as a duplicate only if B is different in both rows.
Example:
FIELD A Field B
10 10
10 10 // This is not duplicate
10 10
10 5 // this is a duplicate
How to to this in a single query
Let's break this down into how you would go about constructing such a query. You don't make it clear whether you're looking for all values of A or all rows but let's assume all values of A initially.
The first step therefore is to create a list of all values of A. This can be done two ways, DISTINCT or GROUP BY. I'm going to use GROUP BY because of what else you want to do:
select a
from your_table
group by a
This returns a single column that is unique on A. Now, how can you change this to give you the unique values? The most obvious thing to use is the HAVING clause, which allows you to restrict on aggregated values. For instance the following will give you all values of A which only appear once in the table
select a
from your_table
group by a
having count(*) = 1
That is the count of all values of A inside the group is 1. You don't want this of course, you want to do this with the column B. You need there to exist more than one value of B in order for the situation you want to identify to be possible (if there's only one value of B then it's impossible). This gets us to
select a
from your_table
group by a
having count(b) > 1
This still isn't enough as you want two different values of B. The above just counts the number of records with the column B. Inside an aggregate function you use the DISTINCT keyword to determine unique values; bringing us to:
select a
from your_table
group by a
having count(distinct b) > 1
To transcribe this into English this means select all unique values of A from YOUR_TABLE that have more than one values of B in the group.
You can use this method, or something similar, to build up your own queries as you create them. Determine what you want to achieve and slowly build up to it.
select FIELD from your_table group by FIELD having count(b) > 1
take in consideration that this will return count of all duplicate
example
if you have values
1
1
2
1
it will return 3 for value 1 not 2
Related
I have this:
SELECT name, value,
MIN(value) as find_min
FROM history
WHERE date_num >= 1609459200
AND date_num <= 1640995200
AND name IN('A')
GROUP BY name
Trying to get the minimum value between dates for each subject separately :
name value
A. 3
B 4
C 9
A 0
C 2
I keep getting this popular error:
column "history.value" must appear in the GROUP BY clause or be used in an aggregate function
I read this must appear in the GROUP BY clause or be used in an aggregate function
and I still do not understand:
Why I have to include in GROUP BY everything? what is the logic?
Why is this not working?
is Min() over (partition by name) better, and if so, how can I get only a single result per name?
EDIT:
If I try:GROUP BY name, find_min it will fail as well, even though in this case he can produce a unique result (the all the same)
That is actually easy to understand.
When you say GROUP BY name, all rows where name is the same are grouped together to form a single result row. Now the original table could contain two rows with the same name, but different value. If you add value to the SELECT list, which of those should be output? On the other hand, determining min(value) for each group is no problem.
Even if there is only a single value for the whole group (like with your find_min), you have to add the column to GROUP BY.
There is actually one exception: if the primary key of a table is in the GROUP BY clause, other columns from that table need not be in GROUP BY, because this proves automatically that there can be no different values.
try like below
SELECT name,
MIN(value) as find_min
FROM history
WHERE date_num >= 1609459200 AND date_num <= 1640995200
GROUP BY name
I removed name in ('A') because your are searching for all name min value so it will restrict just A
To answer your question, GROUP BY groups similar data in a table.
For example this table:
A B C
a d 1
a k 2
b d 3
And you have the query:
SELECT A, B, MIN(C)
FROM t
GROUP BY A
and this would not work you can't give a decisive answer what to do with the entry a k 2 because you don't group by Column B, but you group by column A, is there now two entries but they are different. Therefore you have to group by all non min,max,sum,etc. columns.
As a base example, I have a query that effectively produces a table with a list of values (ID numbers), each of which is attached to a specific category. As a simplified example, it would produce something like this (but at a much larger scale):
IDS
Categories
12345
type 1
12456
type 6
77689
type 3
32456
type 4
67431
type 2
13356
type 2
.....
.....
Using this table, I want to populate another table that gives me a list of ID numbers, with a limit placed on how many of each category are in that list, cross referenced against a sort of range based chart. For instance, if there are 5-15 IDS of type 1 in my first table, I want the new table with the column of IDS to have 3 type 1 IDS in it, if there are 15-30 type 1 IDS in the first table, I want to have 6 type 1 IDS in the new table.
This sort of range based limit would apply to each category, and the IDS would all populate the same column in the new table. The order, or specific IDS that end up in the final table don't matter, as long as the correct number of IDS end up as a part of that final list of ID numbers. This is being used to provide a semi-random sampling of ID numbers based on categories for a sort of QA related process.
If parts of this are unclear I can do my best to explain more. My initial thought was using a variable for a limit clause, but that isnt possible. I have been trying to sort out how to do this with a case statement but I'm really just not making any headway there but I feel like I am at this sort of paper thin wall I just can't break through.
You can use two window functions:
COUNT to keep track of the amount of ids for each category
ROW_NUMBER to uniquely identify each id within each category
Once you have collected these information, it's sufficient to keep all those rows that satisfy either of the following conditions:
count of rows less or equal to 30 >> ranking less or equal to 6
count of rows less or equal to 15 >> ranking less or equal to 3
WITH cte AS (
SELECT IDS,
Categories,
ROW_NUMBER() OVER(ORDER BY IDS PARTITION BY Categories) AS rn
COUNT(IDS) OVER(PARTITION BY Categories) AS cnt
FROM tab
)
SELECT *
FROM cte
WHERE (rn <= 3 AND cnt <= 15)
OR (rn <= 6 AND cnt <= 30)
Note: If you have concerns regarding a specific ordering, you need to fix the ORDER BY clause inside the ROW_NUMBER window function.
suppose I Have below table
A
B
1
one
2
two
1
three
2
four
1
last
for value in A=1
then I need the output as one;three;last
how can I query this in Oracle's SQL?
If you care whether you get the string "one;three;last" or "three;one;last" or some other combination of the three values, you'd need some additional column to order the results by (a database table is inherently unordered). If there is an id column that you're not showing, for example, that could do that, you'd order by id in the listagg.
If you don't care what order the values appear in the result, you could do something like this
select listagg( b, ';' ) within group (order by a)
from your_table
where a = 1
I would like to see a most concise way to do what is outlined in this SO question: Sum values from multiple rows into one row
that is, combine multiple rows while summing a column.
But how to then delete the duplicates. In other words I have data like this:
Person Value
--------------
1 10
1 20
2 15
And I want to sum the values for any duplicates (on the Person col) into a single row and get rid of the other duplicates on the Person value. So my output would be:
Person Value
-------------
1 30
2 15
And I would like to do this without using a temp table. I think that I'll need to use OVER PARTITION BY but just not sure. Just trying to challenge myself in not doing it the temp table way. Working with SQL Server 2008 R2
Simply put, give me a concise stmt getting from my input to my output in the same table. So if my table name is People if I do a select * from People on it before the operation that I am asking in this question I get the first set above and then when I do a select * from People after the operation, I get the second set of data above.
Not sure why not using Temp table but here's one way to avoid it (tho imho this is an overkill):
UPDATE MyTable SET VALUE = (SELECT SUM(Value) FROM MyTable MT WHERE MT.Person = MyTable.Person);
WITH DUP_TABLE AS
(SELECT ROW_NUMBER()
OVER (PARTITION BY Person ORDER BY Person) As ROW_NO
FROM MyTable)
DELETE FROM DUP_TABLE WHERE ROW_NO > 1;
First query updates every duplicate person to the summary value. Second query removes duplicate persons.
Demo: http://sqlfiddle.com/#!3/db7aa/11
All you're asking for is a simple SUM() aggregate function and a GROUP BY
SELECT Person, SUM(Value)
FROM myTable
GROUP BY Person
The SUM() by itself would sum up the values in a column, but when you add a secondary column and GROUP BY it, SQL will show distinct values from the secondary column and perform the aggregate function by those distinct categories.
Okay, I probably could have come up with a better title, but wasn't sure how to word it so let me explain.
Say I have a table with the column 'CODE'. Each record in my table will have either 'A', 'B', or 'C' as it's value in the 'CODE' column. What I would like is to get a count of how many 'A's, 'B's, and 'C's I have.
I know I could accomplish this with 3 different queries, but I'm wondering if there is a way to do it with just 1.
Use:
SELECT t.code,
COUNT(*) AS numInstances
FROM YOUR_TABLE t
GROUP BY t.code
The output will resemble:
code numInstances
--------------------
A 3
B 5
C 1
If a code exists that has not been used, it will not show up. You'd need to LEFT JOIN to the table containing the list of codes in order to see those that don't have any references.