DB2 - select last inserted 5 rows from a table - sql

I have a table that has no indexed rows, nor a specific column...
Let's say "City, PersonName, PersonAge". I need to obtain the last 5 people inserted in that table...
How can I do it in in DB2?
I tried
select * from PEOPLE fetch first 5 rows only
this work perfectly... but no idea how to do it with the LAST rows....


You can't select the last 5 rows inserted, the database doesn't keep track of this. You need some sort of autoincremented ID or timestamp and order by that column descending.

Related

SELECT query to fetch records from table since last fetch based on last updated time

I want to create a select query that fetches 100 records from a table based on the last updated field.
SELECT *
FROM table
WHERE lastupdated > 'xxxx'
ORDER BY lastupdated ASC
LIMIT 100
I will then want to run this query again later with the last updated time from the last record.
What if the 101st record had the same lastupdated value as the 100th record in the first set? This will lead to the next fetch missing that record right?
How do I ensure that I don't duplicate or miss records in the next fetch? Would adding an id column and filtering by id as well solve the issue?

SQL how to select date with limit?

I have a limited history table. It uses composite keys - one of the columns is the timestamp in long.
I want to select/delete rows that are the oldest, and keep the latest 1000 by checking the timestamp. How do I write the statement for such a case?

You can fire delete query escaping 1000 records.
Not in a query will be scape 1000 latest records and rest will be deleted.
Delete from table where Id not in(select top 1000 Id from table order by date desc )

SQLITE3 Insert into the most recent row where 1 column is an exact match

I have this fairly large DB. It contains lots of column. One of the will have a value that I need to select, but the DB has several of that value. How can I insert into a column in the row thats the newest in the DB, with a matching column.

Without knowing the ins and outs of your database, I think you would likely want to select the largest id you have in the auto incrementing row. For instance:
SELECT MAX(UNIQUE_ID) FROM TABLE WHERE MATCHING_COLUMN = MATCHING_VALUE
From there you can take your unique ID and insert into that row.

Return rows in the exact order they were inserted

I have a simple join table with two id columns in SQL Server.
Is there any way to select all rows in the exact order they were inserted?
If I try to make a SELECT *, even if I don't specify an ORDER BY clause, the rows are not being returned in the order they were inserted, but ordered by the first key column.
I know it's a weird question, but this table is very big and I need to check exactly when a strange behavior has begun, and unfortunately I don't have a timestamp column in my table.
UPDATE #1
I'll try to explain why I'm saying that the rows are not returned in 'natural' order when I SELECT * FROM table without an ORDER BY clause.
My table was something like this:
id1 id2
---------------
1 1
2 2
3 3
4 4
5 5
5 6
... and so on, with about 90.000+ rows
Now, I don't know why (probably a software bug inserted these rows), but my table have 4.5 million rows and looks like this:
id1 id2
---------------
1 1
1 35986
1 44775
1 60816
1 62998
1 67514
1 67517
1 67701
1 67837
...
1 75657 (100+ "strange" rows)
2 2
2 35986
2 44775
2 60816
2 62998
2 67514
2 67517
2 67701
2 67837
...
2 75657 (100+ "strange" rows)
Crazy, my table have now millions of rows. I have to take a look when this happened (when the rows where inserted) because I have to delete them, but I can't just delete using *WHERE id2 IN (strange_ids)* because there are "right" id1 columns that belongs to these id2 columns, and I can't delete them, so I'm trying to see when exactly these rows were inserted to delete them.
When I SELECT * FROM table, it returns me ordered by id1, like the above table, and
the rows were not inserted in this order in my table. I think my table is not corrupted because is the second time that this strange behavior happens the same way, but now I have so many rows that I can delete manually like it was on 1st time. Why the rows are not being returned in the order they were inserted? These "strange rows" were definetely inserted yesterday and should be returned near the end of my table if I do a SELECT * without an ORDER BY, isn't it?

A select query with no order by does not retrieve the rows in any particular order. You have to have an order by to get an order.
SQL Server does not have any default method for retrieving by insert order. You can do it, if you have the information in the row. The best way is a primary key identity column:
TableId int identity(1, 1) not null primary key
Such a column is incremented as each row is inserted.
You can also have a CreatedAt column:
CreatedAt datetime default getdate()
However, this could have duplicates for simultaneous inserts.
The key point, though, is that a select with no order by clause returns an unordered set of rows.

As others have already written, you will not be able to get the rows out of the link table in the order they were inserted.
If there is some sort of internal ordering of the rows in one or both of the tables that this link table is joining, then you can use that to try to figure out when the link table rows have been created. Basically, they cannot have been created BEFORE both of the rows containing the PK:s have been created.
But on the other hand you will not be able to find out how long after they have been created.
If you have decent backups, you could try to restore one or a few backups of varying age and then try to see if those backups also contains this strange behaviour. It could give you at least some clue about when the strangeness has started.
But the bottom line is that using just a select, there is now way to get the row out of a table like this in the order they were inserted.

If SELECT * doesn't return them in 'natural' order and you didn't insert them with a timestamp or auto-incrementing ID then I believe you're sunk. If you've got an IDENTITY field, order by that.
But the question I have is, how can you tell that SELECT * isn't returning them in the order they were inserted?
Update:
Based on your update, it looks like there is no method by which to return records as you wish, I'd guess you've got a clustered index on ID1?

Select *, %%physloc%% as pl from table
order by pl desc

How can I retrieve just the last two rows inserted in an SQLite database?

I want to retrieve the last 2 rows inserted into an SQLite database for display in a label. What would be the proper SQLite statement to retrieve these rows?

If you last inserted data has just inserted (maybe in the same method), you can use:
last_insert_rowid
If you like to read the last insert data after, let's say a app re/start, then you need to do some ordering.
If you have a auto-incrementing id row, you can do the following
"SELECT * from your_table ORDER BY your_autoinc_id DESC LIMIT 2"