auto-increment | 易学教程

How to make Primary key Auto increment while using Composite Primary keys in Room persistent library?

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问题 I am using Room persistent library. I have requirement to add two primary keys in one table and one of the primary key should be auto increment. I don't know exact syntax to achieve this. Below is my Model class: @Entity(tableName = "newsPapers", primaryKeys = {"news_paper_id","news_paper_name"}) public class SelectNewsModel { private int news_paper_id; @ColumnInfo(name = "image_url") private String imageUrl; @ColumnInfo(name = "news_paper_name") private String newsPaperName; } I want to make

c# adding row to datatable which has an auto increment column

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问题 I've a datatable, with column A, B, C. I've set column A's "is identity" property to true, but I can't add any row to the table now. The code I'm trying is this: dsA.dtA row = dsA.dtA.NewdtARow(); row.B = 1; row.C = 2; dsA.dtA.Rows.Add(row); I'm getting NoNullAllowedException, but I don't understand why. Column A is PK as well. If I tried to set row.A = 5 (or any similiar) I'll get an error when I try to update the datatable saying "cannot insert explicit value for identity column in table

Problem with auto-incremented “id” column

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问题 My db table looks like this pic. http://prntscr.com/22z1n Recently I've created delete.php page. it works properly but when i deleted 21th user next registered user gets 24th id instead of 21. Is it possible to put newly registered users info to first empty row? (In this situation 21th row) In my registration form, newly registering user can write names of existing users, and be friends with them after registration. For this friendship i have another table that associates id of newly

ID Best Practices for Databases

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问题 I was wondering what the best practices were for building and storing IDs. A few years ago, a professor told me about the dangers of a poorly constructed ID system, using the Social Security Number as an example. In particular, because SSNs do not have any error detection... it is impossible to tell the difference between a 9-digit string and a valid SSN. And now government agencies need things like Last Name + SSN or Birthday + SSN to keep track of your data and ensure its verification. Plus

Is mysql auto increment safe to use as userID?

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问题 I am working on website that allows people to create profiles online. I was wondering if it is the right choice to use MySQL AUTO_INCREMENT ed IDs as my user ids. Also bearing in mind that I might have to duplicate the database across multiple servers one day? e.g. would you use this method for userIds on a website like Twitter or Facebook? I have tried generating userIds with PHP before. I used something like this: function generateID() { $possible = "1234567890"; $code = ""; $characters =

Auto-increment on Azure Table Storage

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I am currently developing an application for Azure Table Storage. In that application I have table which will have relatively few inserts (a couple of thousand/day) and the primary key of these entities will be used in another table, which will have billions of rows. Therefore I am looking for a way to use an auto-incremented integer, instead of GUID, as primary key in the small table (since it will save lots of storage and scalability of the inserts is not really an issue). There've been some discussions on the topic, e.g. on http://social.msdn.microsoft.com/Forums/en/windowsazure/thread

How to manually set seed value as 1000 in MySQL

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问题 I am using MySQL 5. I need to set the seed value as 1000 for my auto increment field. How can I set it? 回答1: To set when creating your table: CREATE TABLE xxx(...) AUTO_INCREMENT = 1000; To set after creating the table: ALTER TABLE xxx AUTO_INCREMENT = 1000; 回答2: If the table already exists, you can do this: ALTER TABLE mytable AUTO_INCREMENT = 1000; But make sure the highest value in the auto_increment column is less than 1000. If you are creating a new table, you can do this: CREATE TABLE

SQL-How to Insert Row Without Auto incrementing a ID Column?

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I have a table that has a forced auto increment column and this column is a very valuable ID that is retained through out the entire app. Sorry to say it was poor development on my part to have this be the auto incrementing column. So, here is the problem. I have to insert into this table an ID for the column that has already been created and removed from the table. Kind of like resurrecting this ID and putting it back into the table. So how can I do this programatically do this without turning the column increment off. Correct me if I am wrong, if I turn it off programatically, It will

Reset autoincrement in Microsoft SQL Server 2008 R2

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I created a primary key to be autoincrement. I added two rows: ID=1, ID=2 I deleted these two rows. I added a new row, but the new row's ID was: ID=3 How can I reset or restart the autoincrement to 1? If you use the DBCC CHECKIDENT command: DBCC CHECKIDENT ("YourTableNameHere", RESEED, 1); But use with CAUTION! - this will just reset the IDENTITY to 1 - so your next inserts will get values 1, then 2, and then 3 --> and you'll have a clash with your pre-existing value of 3 here! IDENTITY just dishes out numbers in consecutive order - it does NOT in any way make sure there are no conflicts! If

Upper limit for autoincrement primary key in SQL Server

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What is the upper limit for an autoincrement primary key in SQL Server? What happens when an SQL Server autoincrement primary key reaches its upper limit? CubanX Joel's answer is correct, it is the upper limit of whatever datatype you use. Here's an example of two of them: int: 2^31-1 (2,147,483,647) bigint: 2^63-1 (9,223,372,036,854,775,807) I have actually hit the limit at a job I worked at. The actual error is: Msg 8115, Level 16, State 1, Line 1 Arithmetic overflow error converting IDENTITY to data type int. Arithmetic overflow occurred. There are a couple fixes to this I can think of off