auto-increment

问题 I have a table with 38.000 records, but without any auto increment column like ID . Now I have to add an ID column, and I'm wondering could there be troubles? 回答1: You problem with definition change to any field is the change is "destructive". It is best to treat changes like this as a data migration. I have not done this with MySQL, but have had to add auto numbering to SQL Server. The basic idea is the same. Check the documentation, as MySQL may have a mechanism for adding aut increment

问题 How do I add auto_increment to an existing column of a MySQL table? 回答1: I think you want to MODIFY the column as described for the ALTER TABLE command. It might be something like this: ALTER TABLE users MODIFY id INTEGER NOT NULL AUTO_INCREMENT; Before running above ensure that id column has a Primary index. 回答2: Method to add AUTO_INCREMENT to a table with data while avoiding “ Duplicate entry ” error: Make a copy of the table with the data using INSERT SELECT: CREATE TABLE backupTable LIKE

问题 One of my tables has the following definition: CREATE TABLE incidents ( id serial NOT NULL, report integer NOT NULL, year integer NOT NULL, month integer NOT NULL, number integer NOT NULL, -- Report serial number for this period ... CONSTRAINT PRIMARY KEY (id), CONSTRAINT UNIQUE (report, year, month, number) ); How would you go about incrementing the number column for every report , year , and month independently ? I'd like to avoid creating a sequence or table for each ( report , year ,

问题 I am trying to maintain an address history table: CREATE TABLE address_history ( person_id int, sequence int, timestamp datetime default current_timestamp, address text, original_address text, previous_address text, PRIMARY KEY(person_id, sequence), FOREIGN KEY(person_id) REFERENCES people.id ); I'm wondering if there's an easy way to autonumber/constrain sequence in address_history to automatically count up from 1 for each person_id . In other words, the first row with person_id = 1 would

问题 I'm experimenting with new Android build system based on Gradle and I'm thinking, what is the best way to autoincrease versionCode with it. I am thinking about two options create versionCode file, read number from it, increase it and write it back to the file parse AndroidManifest.xml, read versionCode from it, increase it and write it back to the AndroidManifest.xml Is there any more simple or suitable solution? Has anyone used one of mentiod options and could share it with me? 回答1: I have

问题 Is there a way to retrieve the auto generated key from a DB query when using a java query with prepared statements. For example, I know AutoGeneratedKeys can work as follows. stmt = conn.createStatement(); stmt.executeUpdate(sql, Statement.RETURN_GENERATED_KEYS); if(returnLastInsertId) { ResultSet rs = stmt.getGeneratedKeys(); rs.next(); auto_id = rs.getInt(1); } However. What if I want to do an insert with a prepared Statement. String sql = "INSERT INTO table (column1, column2) values(?, ?)"

问题 Is there a way to retrieve the auto generated key from a DB query when using a java query with prepared statements. For example, I know AutoGeneratedKeys can work as follows. stmt = conn.createStatement(); stmt.executeUpdate(sql, Statement.RETURN_GENERATED_KEYS); if(returnLastInsertId) { ResultSet rs = stmt.getGeneratedKeys(); rs.next(); auto_id = rs.getInt(1); } However. What if I want to do an insert with a prepared Statement. String sql = "INSERT INTO table (column1, column2) values(?, ?)"

问题 I have a table Messages with columns ID (primary key, autoincrement) and Content (text). I have a table Users with columns username (primary key, text) and Hash. A message is sent by one Sender (user) to many recipients (user) and a recipient (user) can have many messages. I created a table Messages_Recipients with two columns: MessageID (referring to the ID column of the Messages table and Recipient (referring to the username column in the Users table). This table represents the many to many

问题 I have a j2ee application using hibernate with annotation. How do I annotate the Id field in my pojo class to set it as auto increment or auto generated. and in adding the bean do I leave that field in my bean null? 回答1: @Id @GeneratedValue(strategy=GenerationType.AUTO) private int id; and you leave it null ( 0 ) when persisting. ( null if you use the Integer / Long wrappers) In some cases the AUTO strategy is resolved to SEQUENCE rathen than to IDENTITY or TABLE , so you might want to

问题 I'm using MySQL's AUTO_INCREMENT field and InnoDB to support transactions. I noticed when I rollback the transaction, the AUTO_INCREMENT field is not rollbacked? I found out that it was designed this way but are there any workarounds to this? 回答1: Let me point out something very important: You should never depend on the numeric features of autogenerated keys. That is, other than comparing them for equality (=) or unequality (<>), you should not do anything else. No relational operators (<, >)