I've got a data set that looks as follows:
The first column is an auto-increment primary key. The second column is an ID number for whatever, maybe 3 rocks with IDs 1, 2 and 3 respectively. (I probably should have used the standard customer and order example but oh well.) The third column is a date when I threw the rock. I track the date each time the rock is thrown, hence the multiple IDs (the second column) each with a throwing time.
I want a query to return the rock ID and most recent date for each ID. The result of course would have a single record for each ID - the one with the latest access time.
I'm struggling with the possible combination of "DISTINCT", "TOP 1" and "GROUP BY" clauses that gives the result I want.
SELECT id, max(date)
FROM table
GROUP BY id
If you want also the autoincrement row id then
SELECT t1.rowid, t1.id, t1date
FROM table t1
JOIN (SELECT id,max(date) date FROM table1 t2 GROUP BY id) t2 ON t1.id = t2.id AND t1.date = t2.date
Related
There is a table with two fields: Id and Timestamp.
Id is an increasing sequence. Each insertion of a new record into the table leads to the generation of ID(n)=ID(n-1) + 1. Timestamp is a timestamp that, when inserted retroactively, can take any values less than the maximum time of all previous records.
Retroactive insertion is the operation of inserting a record into a table in which
ID(n) > ID(n-1)
Timestamp(n) < max(timestamp(1):timestamp(n-1))
Example of a table:
ID
Timestamp
1
2016.09.11
2
2016.09.12
3
2016.09.13
4
2016.09.14
5
2016.09.09
6
2016.09.12
7
2016.09.15
IDs 5 and 6 were inserted retroactively (their timestamps are lower than later records).
I need a query that will return a list of all ids that fit the definition of insertion retroactively. How can I do this?
It can be rephrased to :
Find every entries for which, in the same table, there is an entry with a lesser id (a previous entry) having a greater timestamp
It can be achieved using a WHERE EXISTS clause :
SELECT t.id, t.timestamp
FROM tbl t
WHERE EXISTS (
SELECT 1
FROM tbl t2
WHERE t.id > t2.id
AND t.timestamp < t2.timestamp
);
Fiddle for MySQL It should work with any DBMS, since it's a standard SQL syntax.
Setup: Postgresql table with a customer_id and a request_id column (+ additional not relevant data).
The rows with customer_id set to NULL work as a fallback/default.
Example what the table looks like:
Goal: I want to select all rows from the table for a given customer (e.g. where customer_id = 2).
For any existent request_id: If there are no entries for the given customer, return the fallback rows (where customer is null).
So the result should look like this:
Any idea how to write the select statement for postgresql? I'm kind of stuck and couldn't really find anything helpful so far. Thanks!
This is a strange requirement.
select t.*
from t
where t.customer_id = 2 or
(t.customer_id is null and
not exists (select 1 from t t2 where t2.request_id = t.request_id and t2.customer_id = 2)
);
For performance, I would recommend an index on (request_id, customer_id).
I need to generate interactive report in Oracle Apex by comparing 2 tables. Each table has Columns: Date, Tag, Number.
Table 1: contains History of the changes of Column: Number and writes on which date the column: Number was changed.
Table 2 : Also has column: Number and column: Date (column: Date which shows different values for column: Number for the different dates of the month).
The Report is being generated when comparing columns "Tag_id" between table 1 and table 2
so we know which value from column: number in table 1 is referring to column: number in table 2. (...where table1.tag=table2.tag).
Table 2 contains date in column: number for every day of the month,
and Table 1 contains date that is changed in column: number once every 1,2,3 or more days.
I want the report to show values from column: Number from Table 1 and to show the values from column: Number from Table 2 while making comparison between table 1 and table 2 by column: Date.
The problem is when in Table 1 there is no date in column:Date which is equal to date in column:Date in Table 2, the Database doesnt know which value for column:Number to return in the Generated Report.
What I want to achieve:
When there is no date match in the columns:Date between Table 1 and Table 2 I want in the Generated report in Apex to return the value from column:Number from Table 2 for the
Date for which there is no match* and the value of column:Number from Table 1 for the closest previous date by using only SQL Query.
Interesting question. I don't know about Apex, but if it were Oracle's MySQL, I'd go along the way of:
SELECT
t2.id,
t2.date,
CASE WHEN t1.date IS NULL
THEN (SELECT table1.number FROM table1 WHERE table1.data <= t2.data ORDER BY table1.data DESC LIMIT 1)
ELSE t1.number
END AS numberT1,
t2.number as numberT2
FROM table2 t2
LEFT JOIN table1 t1 ON t1.date = t2.date
Update a table based on a results of a group by
I've got a tricky update problem I'm trying to solve. There are two tables that contain the same three columns plus additional varied columns, looking like this:
Table1 {pers_id, loc_id, pos, ... }
Table2 {pers_id, loc_id, pos, ... }
None of the fields are unique. The first two fields collectively identify the records in a table (or tables) as belonging to the same entity. Table1 could have 15 records belonging to an entity, and table2 could have 4 records belonging to the same entity. The third column 'pos' is an index from 0 to whatever, and this is the column that I'm trying to update.
In Table1 and in Table2, the pos column begins at 0, and increments based on user selection, so that in the example (15 records in table1 and 4 records in table2), table1 contains 'pos' values of 0 - 14, and Table2 contains 'pos' values of 0-3.
I want to increment the pos field in Table1 with the results of the count of similar entities in Table2. This is the sql statement that correctly gives me the results from table2:
select table2.pers_id, table2.loc_id, count(*) as pos_increment from table2 group by table2.pers_id, table2.loc_id;
The end result of the update, in the example (15 records in table1 and 4 records in table2), would be all records in Table1 of the same entity being incremented by 4 (the result of the specific entity group by). 0 would be changed to 4, 15 to 19, etc.
Is this achievable in a single statement?
Since you only need to increment the pos field the solution is really simple:
update table1 t1
set t1.pos = t1.pos +
(select count(1)
from table2 t2
where t2.pers_id = t1.pers_id
and t2.loc_id = t1.loc_id)
Yes, this is possible, you can use MERGE for some of these upadtes and there are ways to relate values between the update and the subselect. I have done this in the past, but it's tricky and I don't have an existing example.
You can find several examples on this site, some for Oracle and some for other database that will awork with slight modifications.
i have loanTable that contain two field loan_id and status
loan_id status
==============
1 0
2 9
1 6
5 3
4 5
1 4 <-- How do I select this??
4 6
In this Situation i need to show the last Status of loan_id 1 i.e is status 4. Can please help me in this query.
Since the 'last' row for ID 1 is neither the minimum nor the maximum, you are living in a state of mild confusion. Rows in a table have no order. So, you should be providing another column, possibly the date/time when each row is inserted, to provide the sequencing of the data. Another option could be a separate, automatically incremented column which records the sequence in which the rows are inserted. Then the query can be written.
If the extra column is called status_id, then you could write:
SELECT L1.*
FROM LoanTable AS L1
WHERE L1.Status_ID = (SELECT MAX(Status_ID)
FROM LoanTable AS L2
WHERE L2.Loan_ID = 1);
(The table aliases L1 and L2 could be omitted without confusing the DBMS or experienced SQL programmers.)
As it stands, there is no reliable way of knowing which is the last row, so your query is unanswerable.
Does your table happen to have a primary id or a timestamp? If not then what you want is not really possible.
If yes then:
SELECT TOP 1 status
FROM loanTable
WHERE loan_id = 1
ORDER BY primaryId DESC
-- or
-- ORDER BY yourTimestamp DESC
I assume that with "last status" you mean the record that was inserted most recently? AFAIK there is no way to make such a query unless you add timestamp into your table where you store the date and time when the record was added. RDBMS don't keep any internal order of the records.
But if last = last inserted, that's not possible for current schema, until a PK addition:
select top 1 status, loan_id
from loanTable
where loan_id = 1
order by id desc -- PK
Use a data reader. When it exits the while loop it will be on the last row. As the other posters stated unless you put a sort on the query, the row order could change. Even if there is a clustered index on the table it might not return the rows in that order (without a sort on the clustered index).
SqlDataReader rdr = SQLcmd.ExecuteReader();
while (rdr.Read())
{
}
string lastVal = rdr[0].ToString()
rdr.Close();
You could also use a ROW_NUMBER() but that requires a sort and you cannot use ROW_NUMBER() directly in the Where. But you can fool it by creating a derived table. The rdr solution above is faster.
In oracle database this is very simple.
select * from (select * from loanTable order by rownum desc) where rownum=1
Hi if this has not been solved yet.
To get the last record for any field from a table the easiest way would be to add an ID to each record say pID. Also say that in your table you would like to hhet the last record for each 'Name', run the simple query
SELECT Name, MAX(pID) as LastID
INTO [TableName]
FROM [YourTableName]
GROUP BY [Name]/[Any other field you would like your last records to appear by]
You should now have a table containing the Names in one column and the last available ID for that Name.
Now you can use a join to get the other details from your primary table, say this is some price or date then run the following:
SELECT a.*,b.Price/b.date/b.[Whatever other field you want]
FROM [TableName] a LEFT JOIN [YourTableName]
ON a.Name = b.Name and a.LastID = b.pID
This should then give you the last records for each Name, for the first record run the same queries as above just replace the Max by Min above.
This should be easy to follow and should run quicker as well
If you don't have any identifying columns you could use to get the insert order. You can always do it like this. But it's hacky, and not very pretty.
select
t.row1,
t.row2,
ROW_NUMBER() OVER (ORDER BY t.[count]) AS rownum from (
select
tab.row1,
tab.row2,
1 as [count]
from table tab) t
So basically you get the 'natural order' if you can call it that, and add some column with all the same data. This can be used to sort by the 'natural order', giving you an opportunity to place a row number column on the next query.
Personally, if the system you are using hasn't got a time stamp/identity column, and the current users are using the 'natural order', I would quickly add a column and use this query to create some sort of time stamp/incremental key. Rather than risking having some automation mechanism change the 'natural order', breaking the data needed.
I think this code may help you:
WITH cte_Loans
AS
(
SELECT LoanID
,[Status]
,ROW_NUMBER() OVER(ORDER BY (SELECT 1)) AS RN
FROM LoanTable
)
SELECT LoanID
,[Status]
FROM LoanTable L1
WHERE RN = ( SELECT max(RN)
FROM LoanTable L2
WHERE L2.LoanID = L1.LoanID)