I have a Table in the database with 2 Columns containing userIds.
Column A
1
2
3
4
5
Column B
4
2
6
1
7
Now I want to get a list/array containing the distinct Ids.
The expected result will be
[1,2,3,4,5,6,7]
Any idea how to do it?
I am looking for a Ef Core lambda/linq which will run on the database end and not have to fetch the result in the memory and then find the distinct list as that would be costly operation.
you can try this
var ids = Table1.Select( i => i.ColumnA )
.Union( Table2.Select( j => j.ColumnB ) )
.ToList()
Use union:
select col1
from t
union -- on purpose to remove duplicates
select col2
from t;
You would then read the results of the query into your application.
Posting as an answer for further reference:
IList<String> ids = ((from taba in ids select ids) .Union(from tabB in ids select (ids))).ToList();
Related
I have a query I am using IN operator and I want all the rows from in given list as shown in the picture that I want 3 rows for id 1 and one for id 2, but I only get one row for Id = 1 is there any other solution for this.
IN can't do what you want. JOIN instead:
select * from logs
JOIN (values (1),(2),(1),(1)) x (id)
ON logs.id = x.id
I have a table with column with lists like this:
id
[1,2,3,10]
[1]
[2,3,4,9]
The result I would like to have is a table with unlisted values like this:
id2
1
2
3
10
1
2
3
4
9
I have tried different solutions that I found on the web, aws documentation, SO solution, blog post, but without any luck because I have a list in column and not a json object.
Any help is appreciated!
Update (2022): Redshift now supports arrays and allows to "unnest" them easily.
The syntax is simply to have a FROM the_table AS the_table_alias, the_table_alias.the_array AS the_element_alias
Here's an example with the data mentioned in the question:
WITH
-- some table with test data
input_data as (
SELECT array(1,2,3,10) as id
union all
SELECT array(1) as id
union all
SELECT array(2,3,4,9) as id
)
SELECT
id2
FROM
input_data AS ids,
ids.id AS id2
Yields the expected:
id2
---
1
2
3
4
9
1
2
3
10
See here for more details and examples with deeper nesting levels: https://docs.aws.amazon.com/redshift/latest/dg/query-super.html
What is the dataatype of that column?
Redshift does not support arrays, so let me assume this is a JSON string.
Redshift does not provide JSON set-returning functions: we need to unnest manually. Here is one way to do it, if you have a table with a sufficient numbers of rows (at least as many rows as there are elements in the array) - say sometable:
select json_extract_array_element_text(t.id, n.rn) as new_id
from mytable t
inner join (select row_number() over() - 1 as rn from sometable) n
on n.rn < json_array_length(t.id)
I have a set of data that contains 2 sets of identifiers: a unique number for that record, Widget_Number, and the original unique number for the record, Original_Widget_Number. Typically these two values are identical but when a record has been revised, the a new record is created with a new Widget_Number, preserving the old Widget_Number value in Original_Widget_Number. IE SELECT * FROM widgets WHERE Widget_Number != Original_Widget_Number returns all records that have been changed. (Widget_Number increments by 10 for new widgets and by 1 for revised widgets.)
I would like to return all records that were changed as well as the original records related to those records. For example if I had a table containing:
Widget_Number Original_Widget Number More_Data
1: 10 10 Stephen
2: 11 10 Steven
3: 20 20 Joe
I would like a query to return rows 1 & 2. I know I could loop trough this in a higher-level language but is there a straightforward way to do this in MS SQL?
using exists():
select *
from widgets as t
where exists (
select 1
from widgets as i
where i.original_widget_number = t.original_widget_number
and i.widget_number != i.original_widget_number
)
or in()
select *
from widgets as t
where t.original_widget_number in (
select i.original_widget_number
from widgets as i
where i.widget_number != i.original_widget_number
)
The following should get both the records that have changed and the original records:
select w.*
from widgets w
where w.widget_number <> w.original_widget_number or
exists (select 1
from widgets w2
where w.widget_number = w2.original_widget_number and
w2.widget_number <> w2.original_widget_number
);
select * from widget
where original_widget_number in
(select original_widget_number from widget
where widget_number <> original_widget_number)
running a SQL query in access that is giving me matches where A = record 1, and B also = record 1 , C= record 2 and D E and F also = record 2.
I want my results to display (only max Value)
B =record 1
F= record 2. ( this is a matching query)
basically i want to eliminate duplicates and select "distinct" does not seem to be working for me.
SELECT
FEED_2.ID AS FEED_2_ID,
FEED_3.field_ID,
FEED_3.ID AS FEED_3_ID
FROM FEED_2 INNER JOIN FEED_3 ON FEED_2.[field_ID] = FEED_3.[field_ID]
order by FEED_3.ID
im getting results where feed 2 ID #1,3, and 5 all equal feed 3 - ID #1
i only want feed 2, #5 = feed 3 #1. no Dupes
sorry - hope that helps
It's a shot in the dark but, is something like this you are looking for?
SELECT max(Column_With_ABCDEF), Column_With_record from TABLE_NAME GROUP BY Column_With_record;
If this is not what you are asking for, please do edit your question with your table schema and/or the query you are using so we can help.
---------------- EDIT ----------------
Ok so you can try this:
Select max(FEED_2_ID), field_ID , FEED_3_ID
from (
SELECT FEED_2.ID AS FEED_2_ID, FEED_3.field_ID As field_ID, FEED_3.ID AS FEED_3_ID
FROM FEED_2 INNER JOIN FEED_3
ON FEED_2.[field_ID] = FEED_3.[field_ID]
)
GROUP BY FEED_3_ID, field_ID
ORDER BY FEED_3_ID
The main select is going to group the result from the subquery, that way you should not get duplicated values.
Hope this help
I have a tree/hierarchy of groups and a SQL table of items,each associated with a group (ie. each item belongs to a group). I need to select only the rows associated with a given group, or with the groups below.
eg. say this is the group tree:
A
=> B
=> D
=> C
=> E
=> F
Selecting items for group A will return all rows, while selecting for group C will select items belonging in C,E and F (descendants of C).
So far, I am thinking I can implement this in one of two ways:
1. IN list
SELECT * FROM table WERE Group in ('C','E','F')
programatically determining the list of descendants before querying
2. BITWISE operator
SELECT * FROM table WHERE GroupBitMask & 52!=0
(ie. bitwise 'C' + 'E' + 'F' ==bit 3 + bit 5 + bit 6 == 110100 ==52 )
again, this 52 will need to be computed before the query by parsing the group tree.
I guess I can probably enforce a limit of 64 groups max. and use a 64-bit mask for this.
I'm not sure if the database will use an index for this or simply scan all rows to determine the bitwise result?
Are there any other (better?) methods of selecting the rows I need ?
A simple solution is to store the ancestry as part of the row:
Group Path Other columns
A A ...
B AB ...
C AC ...
D ABD ...
E ACE ...
F ACF ...
You can retrieve the base path with single query:
select Path from YourTable where Group = 'C'
Then you can query all descendants like:
select * from YourTable where path like 'AC%'
This performs very well with a primary key on (Group) and an index on (Path).