sql primary key autoincrement

When a primary key is created, if the corresponding column does not have an index, the database will automatically create an index by default. If the column has an index, the primary key will not be created again. Note that the column value must meet the primary

Generate a key generator from a hibernate primary key The Hibernate primary key generator is used to generate the primary key for data table records. There are several common

. For example, in the User Information table, add a field for the user ID. The record used to represent the user's information. Typically, more often than not, the form of a surrogate primary key is used. Moreover, we are accustomed to allowing the primary key field to grow automatically to ensure its uniqueness. Howe

table does not, an error is returned. Otherwise, such If you want to delete the records in the parent table and the child table has records, an error is returned. However, if you use on delete cascade when creating a foreign key constraint , Directly Delete the data associated with the sub-table without an error.If you want to delete the parent table, add cascade constraints. In this case, the foreign key

First look at the label for the primary key mapping:(4) (5) (1)Identifies the name of the property in the class, and actually corresponds to theSetter/gettermethods that conform to the specificationsJavaclass can write property names directly(2)The name of the primary key field in the table(3)Hibernatename of the mappi

Let's take a look at several common primary key generation methods:1, Automatic growth identity: Applicable to MySQL, DB2, and ms SQL Server. It uses the primary key generated by the database to generate a unique ID for long, short, and INT types.Use auto-increment fields of

, because each instance maintains the primary key status, different instances may generate the sameAs a result, duplicate primary keys are abnormal. Therefore, if the same database has multiple instances to access, this method must be avoided.5) identityUse the primary key g

. That's a lot faster than Max plus one. But there is also a problem: when integration with other systems, out of the system of the generation method, it is troublesome to ensure that the maximum value in the self-made table and after the import consistency, and the number of the above mentioned "O" Old data import problem. Therefore, the primary key can be set to the character type in the "Homemade plus on

, auto-incrementing sequence is the best choice of primary key fields. If the user's registered account requires uniqueness and is not empty, it can be used as the primary key field. If you consider horizontal splitting, the auto-incrementing sequence generator architecture is used for easy-to-use and reliable implemen

. MySQL does not support the sequence database (you can use identity). Specify the name of the sequence When hibernate generates a primary key, it looks for sequence and assigns it to the primary key value, the primary key val

max (Id) from processlist) +1, ' A ', ' B ', 1);INSERT INTO ProcesslistValues(null, ' AA ', ' BB ', 1)Execute two INSERT statements before querying the data in the table:SELECT * FROM ProcesslistThe results are as follows:Id Type Name Isuse1 A B 12 AA BB 1A new API function, Sqlite3_last_insert_rowid (), returns the Shaping key for the most recent insert operation. Note that this integer key is always 1 la

assigns it to the primary key value, the primary key value is generated by the database, hibernate is not responsible for maintenance, and you must first create a sequence if you do not specify the sequence name. Use Hibernate's default sequence, named Hibernate_sequence, if you want to create the sequence in the data

database support identity, for example, auto_increment in MySQL and identity in SQL Server. Supported databases include MySQL, SQL Server, DB2, Sybase, and hypersonicsql. Identity does not require Hibernate and user interference. It is easy to use, but it is not convenient to transplant programs between different databases. 5. Sequence Sequence requires that the underlying database support the sequence m

Hibernate primary key Generation policy1. Automatic Growth identityFor MySQL, DB2, MS SQL Server, a database-generated primary key for generating unique identities for long, short, int typesUsing the SQL Server and MySQL self-incr

time. This is much faster than Max plus one. But there is also a problem: when integrating with other systems, it is difficult to ensure that the maximum value in the self-made table is consistent with that in the imported table, in addition, the number type all has the problem of importing old "O" data mentioned above. Therefore, you can set the primary key as the pri