I have a query that essentially tries to get the max serial value for each distinct other_field (simplified example below).
there are a few fields you need to know about
ID text
ser serial
other_field text
For each distinct other_field I want to find the full row with the largest serial value
I basically want to return the whole row but end up having to join on the same table to retrieve what I want (since the group by clause is generally so restrictive). The query I use below
SELECT small_q.id FROM (
SELECT id, MAX(ser) as serial FROM table_name GROUP BY other_field
) max_q JOIN table_name full_t ON small_q.serial = max_q.serial
Is there any way for me to avoid having to join on the same table?
Many thanks in advance
The easy answer would be to use windowing function:
SELECT main.* FROM (
SELECT *, MAX(ser) over (partition by other_field) as serial FROM table_name
) main where main.ser=main.serial
If you are looking for only one row per other_field, I strongly advocate distinct on in Postgres:
SELECT DISTINCT ON (other_field) t.id
FROM table_name t
ORDER BY other_field, ser DESC ;
In Postgres, DISTINCT ON usually has better performance characteristics than other ways of accomplishing the same thing.
Related
There is a table based on ID an those ID's status keys:
The table
I need to write query that will bring higher status key of the same ID. For example; query will bring only the row with status key number 9 for ID number 123. But it will bring the row with status key number 2 for ID number 156.
Hope I managed to explain myself clearly. Please help me with this query.
Use max() aggregation
select id, max(status_key)
from tablename
group by id
You didn't tag your backend, this would work with many backends and older versions of many backends (assuming you have other columns too in your table - otherwise do only group by):
select myTable.*
from myTable
inner join
(select id, max(statusKey) as statusKey
from myTable
group by id) tmp on myTable.id = tmp.id and myTable.statusKey = tmp.statusKey;
I have an oracle database table with a lot of columns. I'd like to count the number of fully unique rows. The only thing I could find is:
SELECT COUNT(DISTINCT col_name) FROM table;
This however would require me listing all the columns and I haven't been able to come up with syntax that will do that for me. I'm guessing the reason for that is that this query would be very low performance? Is there a recommended way of doing this?
How about
SELECT COUNT(*)
FROM (SELECT DISTINCT * FROM Table)
It depends on what you are trying to accomplish.
To get a count of the distinct rows by specific column, so that you know what data exists, and how many of that distinct data there are:
SELECT DISTINCT
A_CODE, COUNT(*)
FROM MY_ARCHV
GROUP BY A_CODE
--This informs me there are 93 unique codes, and how many of each of those codes there are.
Another method
--How to count how many of a type value exists in an oracle table:
select A_CDE, --the value you need to count
count(*) as numInstances --how many of each value
from A_ARCH -- the table where it resides
group by A_CDE -- sorting method
Either way, you get something that looks like this:
A_CODE Count(*)
1603 32
1600 2
1605 14
I think you want a count of all distinct rows from a table like this
select count(1) as c
from (
select distinct *
from tbl
) distinct_tbl;
SELECT DISTINCT **col_name**, count(*) FROM **table_name** group by **col_name**
Can i select all rows that have same column value (for example SSN field) but display them all separably. ?
I've searched for this answer but they all have "count(*) and group by" section that demands the rows to be exactly same.
Try This:
SELECT A, B FROM MyTable
WHERE A IN
(
SELECT A FROM MyTable GROUP BY A HAVING COUNT(*)>1
)
I have done with SQL server. But hope this is what you need
Here is another approach, which only references the table once, using an analytic function instead of a subquery to get the duplicate counts It might be faster; it also might not, depending on the particular data.
SELECT * FROM (
SELECT col1, col2, col3, ssn, COUNT(*) OVER (PARTITION BY ssn) ssn_dup_count
)
WHERE ssn_dup_count > 1
ORDER BY ssn_dup_count DESC
SELECT
*
FROM
MyTable
WHERE
EXISTS
(
SELECT
NULL
FROM
MyTable MT
WHERE
MyTable.SameColumnName = MT.SameColumnName
AND MyTable.DifferentColumnName <> MT.DifferentColumnName)
This will fetch the required data and show them in order so that we can see the grouped data together.
SELECT * FROM TABLENAME
WHERE SSN IN
(
SELECT SSN FROM TABLENAMEGROUP BY SSN HAVING COUNT(SSN)>1
)
ORDER BY SSN
Here SSN is the column names fro which similar value check is done.
If i perform a standard query in SQLite:
SELECT * FROM my_table
I get all records in my table as expected. If i perform following query:
SELECT *, 1 FROM my_table
I get all records as expected with rightmost column holding '1' in all records. But if i perform the query:
SELECT *, COUNT(*) FROM my_table
I get only ONE row (with rightmost column is a correct count).
Why is such results? I'm not very good in SQL, maybe such behavior is expected? It seems very strange and unlogical to me :(.
SELECT *, COUNT(*) FROM my_table is not what you want, and it's not really valid SQL, you have to group by all the columns that's not an aggregate.
You'd want something like
SELECT somecolumn,someothercolumn, COUNT(*)
FROM my_table
GROUP BY somecolumn,someothercolumn
If you want to count the number of records in your table, simply run:
SELECT COUNT(*) FROM your_table;
count(*) is an aggregate function. Aggregate functions need to be grouped for a meaningful results. You can read: count columns group by
If what you want is the total number of records in the table appended to each row you can do something like
SELECT *
FROM my_table
CROSS JOIN (SELECT COUNT(*) AS COUNT_OF_RECS_IN_MY_TABLE
FROM MY_TABLE)
I have a need to check a live table against a transactional archive table and I'm unsure of the fastest way to do this...
For instance, let's say my live table is made up of these columns:
Term
CRN
Fee
Level Code
My archive table would have the same columns, but also have an archive date so I can see what values the live table had at a given date.
Now... How would I write a query to ensure that the values for the live table are the same as the most recent entries in the archive table?
PS I'd prefer to handle this in SQL, but PL/SQL is also an option if it's faster.
SELECT term, crn, fee, level_code
FROM live_data
MINUS
SELECT term, crn, fee, level_code
FROM historical_data
Whats on live but not in historical. Can then union to a reverse of this to get whats in historical but not live.
Simply:
SELECT collist
FROM TABLE A
minus
SELECT collist
FROM TABLE B
UNION ALL
SELECT collist
FROM TABLE B
minus
SELECT collist
FROM TABLE A;
You didn't mention how rows are uniquely identified, so I've assumed you also have an "id" column:
SELECT *
FROM livetable
WHERE (term, crn, fee, levelcode) NOT IN (
SELECT FIRST_VALUE(term) OVER (ORDER BY archivedate DESC)
,FIRST_VALUE(crn) OVER (ORDER BY archivedate DESC)
,FIRST_VALUE(fee) OVER (ORDER BY archivedate DESC)
,FIRST_VALUE(levelcode) OVER (ORDER BY archivedate DESC)
FROM archivetable
WHERE livetable.id = archivetable.id
);
Note: This query doesn't take NULLS into account - if any of the columns are nullable you can add suitable logic (e.g. NVL each column to some "impossible" value).
unload to table.unl
select * from table1
order by 1,2,3,4
unload to table2.unl
select * from table2
order by 1,2,3,4
diff table1.unl table2.unl > diff.unl
Could you use a query of the form:
SELECT your columns FROM your live table
EXCEPT
SELECT your columns FROM your archive table WHERE archive date is most recent;
Any results will be rows in your live table that are not in your most recent archive.
If you also need rows in your most recent archive that are not in your live table, simply reverse the order of the selects, and repeat, or get them all in the same query by performing a (live UNION archive) EXCEPT (live INTERSECTION archive)