update primary key sql

Org.hibernate.id.IncrementGenerator class, using the Select Max (idcolumnname) from TableName statement to get the primary key maximum value. This method is declared as synchronized, so there is no problem inside a standalone Java virtual machine, however, the same value may be fetched when multiple JVMs concurrently access the database select Max, and then insert occurs dumplicate Entry's error. So there

-compulsive disorder). Besides, if I delete the primary key with ID 2. It's like this: 1, 3, 4... 10000, 3000000000001; don't you think it looks bad, of course, only obsessive-compulsive disorder.Summary: I think that as long as you grasp the uniqueness of the primary key, there are many ways to choose how to generate

Database:Warehouse where data is stored, data is classified by tableFeatures: mass storage, fast searching, control of concurrency problems, security, data integrity (the data stored in the database is correct and true)database software: DBSM Database Management SystemCommon database software: MySQL MSSQL Server Oracle AccessSQL: Structured Query Language Structured Query Language features: Simple language, easy to learn and easy to use.SQL Server: is a large network-based database software. The

Sub-query, also called nested query.A query statement is used as a result set for other SQL statements, just as a query statement that is treated as a result set is called a subquery, as with a normal table.There are two types of sub-queries:One is to return only a single-valued subquery, at which point it can be used where a single value can be used, when a subquery can be considered a function that has a return value;Another is a subquery that retur

Org.hibernate.id.IncrementGenerator class, using the Select Max (idcolumnname) from TableName statement to get the primary key maximum value. This method is declared as synchronized, so there is no problem inside a standalone Java virtual machine, however, the same value may be fetched when multiple JVMs concurrently access the database select Max, and then insert occurs dumplicate Entry's error. So there

) from TableName statement to get the primary key maximum value. This method is declared as synchronized, so there is no problem inside a standalone Java virtual machine, however, the same value may be fetched when multiple JVMs concurrently access the database select Max, and then insert occurs dumplicate Entry's error. So there can only be one hibernate application process to access the database, otherwis

) from TableName statement to get the primary key maximum value. This method is declared as synchronized, so there is no problem inside a standalone Java virtual machine, however, the same value may be fetched when multiple JVMs concurrently access the database select Max, and then insert occurs dumplicate Entry's error. So there can only be one hibernate application process to access the database, otherwis

. Hibernate calls the generate () method in the org. hibernate. id. IncrementGenerator class and uses the select max (idColumnName) from tableName statement to obtain the maximum value of the primary key. This method is declared as synchronized, so there is no problem in an independent Java Virtual Machine. However, when multiple JVMs concurrently access the database select max, the same value may be obt

while the foreign key is being constructed.(4) When updating a primary key record, there is also a selection of cascading updates and rejected executions.3.2 SettingsSelect the table, right-click: Design, select the field that you want to set the foreign key, choose Relationships, select Add, select the right ellipsis

This article mainly introduces the difference and connection between the primary key and the foreign key in MySQL. it is the basic knowledge in MySQL beginners. if you need it, you can refer to the relationship between the primary key and the foreign

Both the Primary key and the unique key are unique constraints. But there's a big difference:1, Primary key 1 or more columns must be NOT NULL, if column is null, when the Primary key i

`sequence` ( `name` varchar(50) NOT NULL, `id` bigint(20) unsigned NOT NULL DEFAULT '0', PRIMARY KEY (`name`) ) ENGINE=InnoDB; Note that the ID field is not self-increasing, nor is it a primary key. Before using it, we need to insert some initialization data first: INSERT INTO `sequence` (`name`) VALUES (

SQL> alter Table t drop constraint pk_ I; table altered. SQL> conn y/123 SQL> @ $ ORACLE_HOME/rdbms/admin/utlexcpt. SQL Table created. SQL> alter table t add constraint pk_ I primary key