Suppose I have a table(a relationship) like
MyTab(ID1,ID2,IsMarked, data,....)
the sample data maybe looks like:
1, 1, 1, ...
1, 2, 0, ...
1, 3, 0, ...
2, 34, 1, ...
3, 4, 0, ...
4, 546, 0, ...
4, 8, 0, ...
Only one could be marked for each ID1. I want to get data marked as 1 for all Entities ID1. If there is no marked record, get the first one or any one of them.
For above sample data, the result should be:
1, 1, 1, ...
2, 34, 1, ...
3, 4, 0, ...
4, 546, 0, ...
Union could be a solution, but is too long and may have bad performance.
My idea is to sort the data by ID1 and IsMarked desc, the get the first 1 for each ID1, but how to write a SQL for this case?
For Only one could be marked for each ID1 the following should work:
;with cte as (
select *, rn=row_number() over (partition by ID1 order by IsMarked desc)
)
select *
from cte
where rn=1
Shot in the dark:
SELECT A.*
FROM MYTAB A
LEFT JOIN (
SELECT MAX(ID2) AS MAXID2, ID1
FROM MYTAB
WHERE ISMARKED=1
GROUP BY ID1
) B ON A.ID2=B.MAXID2 AND A.ID1=B.ID1
LEFT JOIN (
SELECT MAX(ID2) AS MAXID2, ID1
FROM MYTAB
WHERE ISMARKED=0
GROUP BY ID1
) C ON A.ID2=C.MAXID2 AND A.ID1=C.ID1
WHERE
(B.ID1 IS NOT NULL)
OR
(B.ID1 IS NULL AND C.ID1 IS NOT NULL);
Related
I want to filter out the duplicates from a BigQuery array. I also need the order of the elements to be preserved. The docs mention that this can be done by combining SELECT DISTINCT with UNNEST. However, it doesn't mention any ordering behavior. I ran this query and got the desired ordering of [5, 3, 1, 4, 10, 8].
WITH an_array AS (
SELECT [5, 5, 3, 1, 4, 4, 10, 8, 5, 1] AS nums
)
SELECT
ARRAY((
SELECT DISTINCT num
FROM UNNEST(nums) num
))
FROM an_array;
I don't know if that's coincidence or if that ordering is guaranteed. I also tried adding WITH OFFSET with an ORDER BY to specify the order explicitly, but in that case I get Query error: ORDER BY clause expression references table alias offset which is not visible after SELECT DISTINCT.
You should always be explicit about ordering if you care about it:WITH an_array AS (
WITH an_array as (
SELECT [5, 5, 3, 1, 4, 4, 10, 8, 5, 1] AS nums
)
SELECT ARRAY((SELECT num
FROM UNNEST(nums) num WITH OFFSET o
GROUP BY num
ORDER BY MIN(o)
)
)
FROM an_array;
This is a beginner-question relating arrays. I hope the answer is simple.
The example is taken from Oracle Spatial, but I think it is valid for all arrays.
I have this SELECT:
SELECT
D.FID
, D.GEOM.SDO_ELEM_INFO -- column GEOM contains spatial data
FROM
my_table D
I get this result:
73035 MDSYS.SDO_ELEM_INFO_ARRAY(1, 2, 1)
73036 MDSYS.SDO_ELEM_INFO_ARRAY(1, 4, 3, 1, 2, 1, 11, 2, 2, 19, 2, 1)
73037 MDSYS.SDO_ELEM_INFO_ARRAY(1, 2, 1)
Now I want to SELECT all rows where (1,2,1) is defined:
SELECT
D.FID
, D.GEOM.SDO_ELEM_INFO
FROM
my_table D
WHERE
-- Pseudo-Code is following
D.GEOM.SDO_ELEM_INFO is "(1, 2, 1)";
So, in simple words: "array_from_row = defined_array".
I found a lot about IMPLODE and TABLE and COLLECT etc. But how to define a clause on two arrays?
Thanks for help!
Try IN clause, you can also use both
SELECT
D.FID
, D.GEOM.SDO_ELEM_INFO
FROM
my_table D
WHERE
D.GEOM.SDO_ELEM_INFO in (1, 2, 1) or ( D.GEOM.SDO_ELEM_INFO = 1 or D.GEOM.SDO_ELEM_INFO = 2 or D.GEOM.SDO_ELEM_INFO = 3);
I have a table with subsets. How to find reader id's with the same subsets as given id? For example:
Input reader = 4
The expected output: reader 1 and 5.
Subsets size is not always = 3 as in the example it can be dynamic. What is correct SQL query?
declare #t table(
reader int not null,
book int,
pages int
)
insert into #t (reader, book, pages)
select 1, 1, 100 union
select 1, 2, 201 union
select 1, 3, 301 union
select 2, 1, 100 union
select 2, 3, 101 union
select 2, 3, 301 union
select 3, 1, 100 union
select 3, 2, 101 union
select 3, 3, 301 union
select 4, 1, 100 union
select 4, 2, 201 union
select 4, 3, 301 union
select 5, 1, 100 union
select 5, 2, 201 union
select 5, 3, 301
select * from #t
This is a bit of a pain, but you can use a self-join:
with t as (
select t.*, count(*) over (partition by reader) as cnt
from #t t
)
select t.reader
from t left join
t t2
on t2.book = t.book and
t2.pages = t.pages and
t2.cnt = t.cnt and
t2.reader = 4
group by t.reader, t.cnt
having count(*) = t.cnt and
count(*) = count(t2.reader);
The left join is needed to avoid a subsetting relationship. That is, having all the books for "4" plus additional books.
This is a generic approach to handle relational division. It checks if set x contains all elements from set y (and perhaps more):
with reqd as (
select book, pages
from #t
where reader = 1
)
select t.reader
from #t as t
inner join reqd on t.book = reqd.book and t.pages = reqd.pages
group by t.reader
having count(reqd.book) = (select count(*) from reqd)
I've got a Table that stores messages
like this:
codMsg, message, anotherCod
1, 'hi', 1
2, 'hello', 1
3, 'wasup', 1
4, 'yo', 2
5, 'yeah', 2
6, 'gogogo', 3
I was wondering if is possible to select top 1 of each anotherCod
What I expect:
1, 'hi', 1
4, 'yo', 2
6, 'gogogo', 3
I want the whole line, not just the number of the anotherCod, so group by should not work
select mytable.*
from mytable
join (select min(codMsg) as codMsg, anotherCod from mytable group by 2) x
on mytable.codMsg = x.codMsg
SQL Server 2005+, Oracle :
SELECT codMsg,
message,
anotherCod
FROM
(
SELECT codMsg,
message,
anotherCod,
RANK() OVER (PARTITION BY anotherCod ORDER BY codMsg ASC) AS Rank
FROM mytable
) tmp
WHERE Rank = 1
SELECT
*
FROM
myTable
WHERE
codMSG = (SELECT MIN(codMsg) FROM myTable AS lookup WHERE anotherCod = myTable.anotherCod)
How can I limit a result set to n distinct values of a given column(s), where the actual number of rows may be higher?
Input table:
client_id, employer_id, other_value
1, 2, abc
1, 3, defg
2, 3, dkfjh
3, 1, ldkfjkj
4, 4, dlkfjk
4, 5, 342
4, 6, dkj
5, 1, dlkfj
6, 1, 34kjf
7, 7, 34kjf
8, 6, lkjkj
8, 7, 23kj
desired output, where limit distinct=5 distinct values of client_id:
1, 2, abc
1, 3, defg
2, 3, dkfjh
3, 1, ldkfjkj
4, 4, dlkfjk
4, 5, 342
4, 6, dkj
5, 1, dlkfj
Platform this is intended for is MySQL.
You can use a subselect
select * from table where client_id in
(select distinct client_id from table order by client_id limit 5)
This is for SQL Server. I can't remember, MySQL may use a LIMIT keyword instead of TOP. That may make the query more efficient if you can get rid of the inner most subquery by using the LIMIT and DISTINCT in the same subquery. (It looks like Vinko used this method and that LIMIT is correct. I'll leave this here for the second possible answer though.)
SELECT
client_id,
employer_id,
other_value
FROM
MyTable
WHERE
client_id IN
(
SELECT TOP 5
client_id
FROM
(
SELECT DISTINCT
client_id
FROM
MyTable
) SQ
ORDER BY
client_id
)
Of course, add in your own WHERE clause and ORDER BY clause in the subquery.
Another possibility (compare performance and see which works out better) is:
SELECT
client_id,
employer_id,
other_value
FROM
MyTable T1
WHERE
T1.code IN
(
SELECT
T2.code
FROM
MyTable T2
WHERE
(SELECT COUNT(*) FROM MyTable T3 WHERE T3,code < T2.code) < 5
)
-- Using Common Table Expression in Microsoft SQL Server.
-- LIMIT function does not exist in MS SQL.
WITH CTE
AS
(SELECT DISTINCT([COLUMN_NAME])
FROM [TABLE_NAME])
SELECT TOP (5) [[COLUMN_NAME]]
FROM CTE;
This works for MS SQL if anyone is on that platform:
SET ROWCOUNT 10;
SELECT DISTINCT
column1, column2, column3,...
FROM
Table1
WHERE ...