In some cases, I want to copy some rows in the the same order that original rows. So I would like can order the original rows by ID and later create the new records in the same way.
But I don't know if EF ensure the order of the inserts or not, or if there are some kind of configuration that can ensure that.
One solution could be use a transactión, do a SaveChanges() after add the new row and finally commit the transaction. But I would like to avoid this because it would make me to use many SaveChanges() and also if for some reason the action can't be done because of some reason, the IDs that are assigned would be lose and I would have gaps. Really this second reason it is not important but I would like to avoid gaps if it is possible.
Thanks.
if your account has sufficient permissions:
ExecuteSqlCommand(#"SET IDENTITY_INSERT [dbo].[TABLENAME] ON");
//do insert with original ids, meaning the primary key can't already exist in the target table
context.SaveChanges();
context.Database.ExecuteSqlCommand(#"SET IDENTITY_INSERT [dbo].[TABLENAME] OFF");
Related
I use SQL Server with ASP.NET Core and EF Core. After each record is added, the identity column's value jumps about by 1000 and creates a gap between current row and the last previously added row.
Questions
Is there any way to prevent this?
How to delete those gaps that have been created before?
If I use GUID for key columns to prevent that issue, is there a problem (performance or each other problem)?
Is it way on the server side that with EF Core could handle it (each some way)?
Thank you in advance for your helps...
For the reason for 1000-value gaps, see Aaron Bertrand's answer
It doesn't really make sense to "want" to delete the gaps. The content of an identity column contains no semantic information. It correlates to nothing "in the world" outside the database. The gaps are as meaningless as the values themselves.
I don't see how a uniqueidentifier would "prevent" that issue. A uniqueidentifier may be "meaningfully" sortable (if you use newsequentialid()), but there's no sense in which any particular value is "one more" than a previous value.
You can certainly try to build your own key generating algorithm that does not produce gaps, but you will run into concurrency issues (also mentioned by Mr Bertrand).
workaround trick:
CREATE OR ALTER TRIGGER TGR_Transaction_Identity_Fix
ON [dbo].[TBL_Transaction]
FOR INSERT
AS
BEGIN
DECLARE #RESEEDVAL INT
SELECT #RESEEDVAL = MAX(TransactionId) FROM [dbo].[TBL_Transaction]
DBCC CHECKIDENT([TBL_Transaction], RESEED, #RESEEDVAL)
END
this triger will reset identity on each insert
Hopefully an easy question for someone with more experience than me. I have a stored procedure that Inserts records into a table. Like all databases that I have worked with, when you insert a record it inserts it into the bottom of the table. I would like to insert it to the top of the table and then move all the existing records down by one (I assume this would happen automatically with the insert).
I want to to do this because I'm using the 'Top #' keyword. I am pretty sure that I could just leave it the way it is, and instead of using the 'Top" keyword, I could use the 'Bottom" keyword. But I want to make it easier for people reading it that aren't familiar with it, so they can instantly see the newest entries. I'm going to keep researching this on my own, but If someone knew off the top of their head and could save me the time that would be appreciated.
is there any incremental id on that table.If yes then create clustered index on that id with descending order
I'm new to postgreSQL, so would really appreciate any pointers from the community.
I am updating some functionality in the CMS of a pretty old site I've just inherited. Basically, I need the ID of an article before it is inserted into the database. Is there anyway anyway to check the next value that will be used by a sequence before a database session (insert) has begun?
At first I thought I could use SELECT max(id) from tbl_name, however as the id is auto incremented from a sequence and articles are often deleted, it obviously won't return a correct id for the next value in the sequence.
As the article isn't in the database yet, and a database session hasn't started, it seems I can't use the currval() functionality of postgreSQL. Furthermore if I use nextval() it auto increments the sequence before the data is inserted (the insert also auto-incrementing the sequence ending up with the sequence being doubly incremented).
The way I am getting around it at the moment is as follows:
function get_next_id()
{
$SQL = "select nextval('table_id_seq')";
$response = $this->db_query($SQL);
$arr = pg_fetch_array($query_response, NULL, PGSQL_ASSOC);
$id = (empty($arr['nextval'])) ? 'NULL' : intval($arr['nextval']);
$new_id = $id-1;
$SQL = "select setval('table_id_seq', {$new_id})";
$this->db_query($SQL);
return $id;
}
I use SELECT nextval('table_id_seq') to get the next ID in the sequence. As this increments the sequence I then immediately use SELECT setval('table_id_seq',$id) to set the sequence back to it's original value. That way when the user submits the data and the code finally hits the INSERT statement, it auto increments and the ID before the insert and after the insert are identical.
While this works for me, I'm not too hot on postgreSQL and wonder if it could cause any problems down the line, or if their isn't a better method? Is there no way to check the next value of a sequence without auto-incrementing it?
If it helps I'm using postgresql 7.2
Folks - there are reasons to get the ID before inserting a record. For example, I have an application that stores the ID as part of the text that is inserted into another field. There are only two ways to do this.
1) Regardless of the method, get the ID before inserting to include in my INSERT statement
2) INSERT, get the the ID (again, regardless of how (SELECT ... or from INSERT ... RETURNING id;)), update the record's text field that includes the ID
Many of the comments and answers assumed the OP was doing something wrong... which is... wrong. The OP clearly stated "Basically, I need the ID of an article before it is inserted into the database". It should not matter why the OP wants/needs to do this - just answer the question.
My solution opted to get the ID up front; so I do nextval() and setval() as necessary to achieve my needed result.
Disclaimer: Not sure about 7.2 as I have never used that.
Apparently your ID column is defined to get its default value from the sequence (probably because it's defined as serial although I don't know if that was available in 7.x).
If you remove the default but keep the sequence, then you can retrieve the next ID using nextval() before inserting the new row.
Removing the default value for the column will require you to always provide an ID during insert (by retrieving it from the sequence). If you are doing that anyway, then I don't see a problem. If you want to cater for both scenarios, create a before insert trigger (does 7.x have them?) that checks if the ID column has a value, if not retrieve a new value from the sequence otherwise leave it alone.
The real question though is: why do you need the ID before insert. You could simply send the row to the server and then get the generated id by calling curval()
But again: you should really (I mean really) talk to the customer to upgrade to a recent version of Postgres
I am obtaining a json array from a url and inserting data into a table. Since the contents of the url are subject to change, I want to make a second connection to a url and check for updates and insert new records in y table using sqlite3.
The issues that I face are:
1) My table doesn't have a primary key
2) The url lists the changes on the same day. Hence, if I run my app multiple times, when I insert values in my database, I get duplicate entries. I want to keep a check for the day duplicated entries that should be removed. The problem can be solved by adding a constraint, but since the url itself has duplicated values, I find it difficult.
The only way I can see you can do it if you have no primary key or something you can use that is unique to each record, is when you get your new data in you go through the new entries where for each one you check if the exact same data exists in the database already. If it doesn't then you add it, if it does then you skip over it.
You could even do something like create a unique key yourself for each entry which is a concatenation of each column of the table. That way you can quickly do the check for if the entry already exists in the database.
I see two possibilities depending on your setup:
You have a column setup as UNIQUE (this can be through a PRIMARY KEY or not). In this case, you can use the ON CONFLICT clause:
http://www.sqlite.org/lang_conflict.html
If you find this construct a little confusing, you can instead use "INSERT OR REPLACE" or "INSERT OR IGNORE" as described here:
http://www.sqlite.org/lang_insert.html
You do not have a column setup as UNIQUE. In this case, you will need to SELECT first to verify for duplicate data, and based on the result INSERT, UPDATE, or do nothing.
A more common & robust way to handle this is to associate a timestamp with each data item on the server. When your app interrogates the server it provides the timestamp corresponding to the last time it synced. The server then queries its database and returns all values that are timestamped later than the timestamp provided by the app. Then it also returns a new timestamp value for the app to store, to use on the next sync.
this is my first time using SQL at all, so this might sound basic. I'm making an iPhone app that creates and uses a sqlite3 database (I'm using the libsqlite3.dylib database as well as importing "sqlite3.h"). I've been able to correctly created the database and a table in it, but now I need to know the best way to get stuff back from it.
How would I go about retrieving all the information in the table? It's very important that I be able to access each row in the order that it is in the table. What I want to do (if this helps) is get all the info from the various fields in a single row, put all that into one object, and then store the object in an array, and then do the same for the next row, and the next, etc. At the end, I should have an array with the same number of elements as I have rows in my sql table. Thank you.
My SQL is rusty, but I think you can use SELECT * FROM myTable and then iterate through the results. You can also use a LIMIT/OFFSET(1) structure if you do not want to retrieve all elements at one from your table (for example due to memory concerns).
(1) Note that this can perform unexpectedly bad, depending on your use case. Look here for more info...
How would I go about retrieving all the information in the table? It's
very important that I be able to access each row in the order that it
is in the table.
That is not how SQL works. Rows are not kept in the table in a specific order as far as SQL is concerned. The order of rows returned by a query is determined by the ORDER BY clause in the query, e.g. ORDER BY DateCreated, or ORDER BY Price.
But SQLite has a rowid virtual column that can be used for this purpose. It reflects the sequence in which the rows were inserted. Except that it might change with a VACUUM. If you make it an INTEGER PRIMARY KEY it should stay constant.
order by rowid