I have a table with three columns as follows:
id INTEGER name TEXT value REAL
How can I select the value at the maximum id?
Get the records with the largest IDs first, then stop after the first record:
SELECT * FROM MyTable ORDER BY id DESC LIMIT 1
Just like the mysql, you can use MAX()
e.g. SELECT MAX(id) AS member_id, name, value FROM YOUR_TABLE_NAME
Try this:
SELECT value FROM table WHERE id==(SELECT max(id) FROM table));
If you want to know the query syntax :
String query = "SELECT MAX(id) AS max_id FROM mytable";
Related
A simple select * from mytable will return below rows. I don't know how to draw table in post so I am adding the image
As I mentioned in the question title:
(i) show first n rows sorted by one column (can be achieved using order by)
(ii) but they should be unique by another column (unique by collectionID column)
select * from mytable
order by lastAccessTime DESC;
this sorts the table in descending order according to their lastAccessTime as shown in below image:
Now I want to filter these rows according to their collectionID. So only 1 row per collectionID. I have added the image. The strikethrough rows should be removed.
Also, First n rows (lets say 30) should be returned.
I am using Android Room ORM which uses SQLite but to get the desired result set I have to write the correct query.
I think you need a window function filter here. Which will assign a row number based on collectionID and then you can just fetch only 1 row per collectionID. You may give a try to -
SELECT *
FROM (SELECT *, ROW_NUMBER() OVER(PARTITION BY collectionID ORDER BY ID DESC) RN
FROM mytable) T
WHERE RN = 1
LIMIT 30;
The key idea is to "filter" the data with one query which is the source of another query. A window function can be used as in the other answer, but a basic sub-query is also sufficient:
SELECT *
FROM mytable
INNER JOIN
(SELECT Max(id) AS singleID, collectionID
FROM mytable
GROUP BY collectionID) AS filter
ON mytable.id = filter.singleID
ORDER BY lastAccessTime DESC
LIMIT 30;
I have a table which has one primary key integer:
CREATE TABLE TBL (ID INTEGER PRIMARYKEY,ZID INTEGER)
That zid integer field that must be incremented from the previous one found in the database.
I could do something like that:
INSERT INTO TBL (zid) VALUES ((SELECT MAX(zid) + 1 FROM TBL));
However, the value of that integer field will, at some point, reset to zero. Therefore I want to increment from the last entry, not necessarily the maximum in the entire table.
How can I do that? A trigger?
Thanks.
how about a query like:
SELECT zid + 1 FROM TBL ORDER BY id DESC LIMIT 1
with this select query you will only get the value from the last line (+1)
When i query with :
select code,volatility from big_sh order by volatility asc;
I get right result,when adding rowid in the statement ,the rowid is matched with table big_sh,can i create a new rowid matched with my new result of select ?
select rowid,code,volatility from big_sh order by volatility asc;
The _id column in my database is an INTEGER PRIMARY KEY, so it is an auto-incrementing column.
The problem is that now I deleted a row, and the column didn't update the auto-incrementing number.
Is there a way to make the _id column update, so there wouldn't be holes in the sequence?
Thank you very much in advance.
No. This is not how it is intended to be used. Don't mess with the primary key! There will be gapes. The id is just a unique identifier.
If you need a rank then you can do that
select t.*, #rank := #rank + 1 as gapless_rank
from your_table t
cross join (select #rank := 0) r
order by id
To get the nth ID from the table, use a query like this:
SELECT _id
FROM MyTable
ORDER BY _id
LIMIT 1
OFFSET n-1
I have 2 tables, one is indexing the other.
I am querying Table#1, and it has one column (string) that has an ID in it that corresponds to a unique row in Table#2. Im trying to write a query in Sqlite that allows me to retrieve the value from Table#2 if the column value in Table#1 is not an empty string.
Kinda like:
"SELECT TMake,TModel,TTrim,IYear,[%q] AS TPart1 FROM AppGuide WHERE TPart1 != ''"
But instead of retrieving the Index value (TPart1) Id like to get the string from Table#2.
Is this possible?
Any help is appreciated.
You could use a correlated subquery:
SELECT TMake,
TModel,
...,
(SELECT stringvalue
FROM Table2
WHERE Table2.ID = Table1.TPart1)
FROM Table1
WHERE Table1.TPart1 != ''
However, these are rather slow to execute, so you'd better use a join (this returns exactly the same result):
SELECT Table1.TMake,
Table1.TModel,
...,
Table2.stringvalue
FROM Table1 LEFT JOIN Table2 ON Table1.TPart1 = Table2.ID
WHERE Table1.TPart1 != ''
If you don't want to get records from Table1 that have no matching Table2 record, drop the LEFT.