I just want to clarify: if you insert a row to a table in sqlite, it appends it to the table, but -- as I learned -- the table is unordered, so there is really not true way to insert a row into the middle of an "ordered table," right?
Is there even a way to make an ordered table without first created a table and then using '...ORDER BY name/id/etc' (i.e. when you insert something it puts itself in the right place)?
SQLite tables are actually stored in rowid order, but this is unlikely to help you because it is unlikely that there is a gap where you want it.
Furthermore, the order in which rows are stored does not matter because there is no guarantee that this is the order in which they are returned.
When you want to SELECT rows in a specific order, you must use ORDER BY.
If your query is too slow, an index on the sorting column might help.
Related
I have a table that is actually a ranking list. I want to give user a chance to rearrange that top the way he wants, ergo, allow him to move the rows in that table. Should I create a separate column that would hold the place, or can it be done using embedded order in table?
The documentation says:
If a SELECT statement that returns more than one row does not have an ORDER BY clause, the order in which the rows are returned is undefined.
(This is true for all SQL databases.)
So you cannot rely on the order that the rows happen to be stored in; you have to use some value in some table column.
I want to compare the all rows in two tables like below.
TABLEA(ID,NAME,EMAIL,MOBILE,ADDRESS),
TABLEB(ID,NAME,EMAIL,MOBILE,ADDRESS).
Here I have the above tables with 20 columns each in real.
When ever a new row inserted into the tables, I need to compare newly inserted row in two tables, if any column mismatch, put into another table.
For example:
TABLEA(1234,ABCDEF,78699EE7,INDIA)
TABLEB(1234,ABCDEF,78699876,INDIA)
Above Mobile number is not matched, I need to insert column name Mobile into another table.
Please help me on this.
Thank You.
I am sure there are few ways to do it. But one way comes to my mind using SQL only using UNION ALL:
INSERT INTO your_other_table(id, name, email, mobile, address)
SELECT id, name, email, mobile, address
FROM tableA
UNION ALL
SELECT id, name, email, mobile, address
FROM tableB;
However, it is not clear, when you need to run this. Since the INSERT occurs to both tables, does it happen within the same transaction. If so, then the script above can be wrapped in a trigger. If the INSERT occurs in different transactions and always, in the same order (e.g., tableA then tableB), then you can again wrap it in the trigger on tableB. Otherwise, you'll have to run it separately.
Notice, the script above, will compare the entire tables, and not only the newly inserted rows. So If any update happened on any row in either one of the tables, and not the other, that row will be inserted in the third table as well.
I need to enlarge the varchar of one column from 64 to 80. The table is quite big(9m rows). One point that make the alter uncertain is that the column is also indexed.
So if I alter the column, since the column is one of the indexes, will any locking happen for row or table?
Thanks.
Not sure about locking part. but standard recommendation would be to drop the index first and then alter table and again create the index.
drop index [[index name]]
go
alter table t1 [[alter column]]
go
create index [[index name]]
go
So I have a table with data about an image. The table looks something like this...
ROWID|title|description|file_path
The file path contains the name of the image. I want to rename the image to match the ROWID.
How do I get the latest ROWID? I need to also account for rows that have been deleted as I am using this as an autoincremented primary key. Because, if a row within the table has been deleted it is possible for the table to look like this...
1|title A|description A|..\fileA.jpg
2|title B|description B|..\fileB.jpg
5|title E|description E|..\fileE.jpg
7|title G|description G|..\fileG.jpg
On top of that there could be one or more rows that have been deleted so the next ROWID could be 10 for all I know.
I also need to account for an fresh new table or a table that has had all data deleted and the next ROWID could be 1000.
In summary, I guess the real question is; Is there a way to find out what the next ROWID will be?
If you have specified AUTOINCREMENT in primary key field and table is not empty this query will return latest ROWID for table MY_TABLE:
SELECT seq
FROM sqlite_sequence
WHERE name = 'MY_TABLE'
What language? Looks like the c API has the following function:
sqlite3_int64 sqlite3_last_insert_rowid(sqlite3*);
http://www.sqlite.org/c3ref/last_insert_rowid.html
You could also just do:
select MAX(rowid) from [tablename];
Unfortunately neither of these methods completely worked the way I needed them to, but what i did end up doing was....
insert data into table with the fields I needed the rowid for filled with 'aaa'
then updated the rows with the data.
This seemed to solve my current issue. Hopefully it doesn't cause another issue down the road.
I think last_insert_rowid is what you want, usually.
Note that the rowid behavior is different depending on the autoincrement flag - either it will monotonically increase, or it will assume any free id. This will not usually affect any smaller use cases though.
Ok I have a sqlite db, that has roughly 100 rows. It is kind of a strange thing that I'm trying to do, but I need to insert a new row between each of the existing rows.
I have been trying to use the Insert statement as follows, but haven't had any luck:
insert into t1(column1) values("hello") where id%2 == 0
So I'm basically trying to use the %-operator to tell me if the id is even or odd. For every even id number, I'd like to insert a new row.
What am I missing? What can I do differently? How can I insert a new row into every other row and have the index updated as well?
Thanks
Your question assumes that the rows have some kind of built-in order to them, and that you can insert rows between other rows. That's not true.
It is true that rows have an order on disk, and that the id column is usually assigned in order, but that's an implementation detail. When you perform a query, the database is free to return the rows in any order it chooses, unless you specify what you want with an ORDER BY clause.
Now, I'm assuming what you really want is to insert rows between the existing rows in id order. One way to get what you want would look like this:
UPDATE t1 SET id = id * 2
INSERT INTO t1 (id, column) SELECT id+1, "hello" FROM t1
The UPDATE would double the ids of all the existing rows (so 1,2,3 becomes 2,4,6); then the INSERT would perform a query on t1 and use the result to insert a new set of rows with id values one more than the existing rows (so 2,4,6 becomes 3,5,7).
I haven't tested the above statements, so I don't know if they would work or if they require some extra trickery (like a temporary table) since we are querying and updating the same table in one statement. Also I may have made a syntax error.
Don't consider the rows as pre-ordered in the database. A database will store them as they come in, or according to an index. It's your task to order them on retrieval (i.e. when you query for data) according to your needs.