referential integrity

, even if not NULL is not specified on the column, the column must still contain a data value; 2. Only one primary KEY constraint can be defined for each column. 4. Use the Froeign key constraint The Froeign key (foreign key) constraint is primarily used to maintain a consistency relationship between two tables. The foreign key is established mainly by adding the column containing the primary key in one table to another table, which is the foreign key of the other table. Therefore, the foreign

triggered and the trigger deletes all the sub-forum information in the BBS_LANMU table that is part of the newly deleted large section. When the Deltype trigger deletes a record for the datasheet BBS_LANMU, it triggers the trigger DELLANMU on the BBS_LANMU table, which deletes all post information in the Bbs_topic table that is part of the forum that has just been deleted. When the DELLANMU trigger deletes a record for the datasheet bbs_topic and triggers the trigger deltopic, the trigger del

1. Means to achieve data integrityIn SQL Server, there are two main ways to achieve data integrity on the servers: one is to define data integrity when tables are created, mainly to include entity integrity, domain integrity, and cascading referential

Tags: Data taf ASC code simple prim Sync Database key Before encountering such a problem in the project, I give a simple example to illustrate. For example, we have two tables, and one table (department) stores information about the department, such as department ID, department name, and so on, and one table is the employee table (staff), and the employee table must store each employee's department.So the question is, what happens when we delete a record from the department table at this point i

entity attribute cannot be empty, cannot be duplicated, and the constraint is implemented by the specified primary key. Its constraints are systematically enforced. (2) Referential integrity: foreign keys in an entity can be empty, but not wrong, For example, the student management system, the class has not been determined, the students came to report, then had to not split class, But can't write one at wi

Entity integrity1. Define a primary key when building a table Create Table Table Name(Sno int Identity (1,1),Sname nvarchar (20),--Set Primary keyPrimary Key (Sno))2. Add primary key ALTER TABLE nameAdd constraint pk_ table name _snoPrimary KEY (ID)Referential integrity 1. Define foreign keys when building tables CREATE TABLE Table name(Sno int Identity (1,1) primary key,CNO int NOT NULL,Foreign key (CNO

: CREATE TABLE T4 ( ID int primary Key auto_increment, #自动增长, is not recommended. Database migration is inconvenient, not all databases support autogrow, such as Oracle does not support. NAME varchar (100) ); 2.2 Domain (field) integrityA column (that is, a field) of a database table must conform to a specific data type or constraint 1. Type of constraint data: Strong type 2, non-null constraint: NOT NULL 3. Unique constraint: Unique CREATE TABLE T5 ( ID int primary Key auto_increment, USERNAME

Tags: DCL delete com efault prim alt commit EVO controlFour statements:1. Data definition statements: ddl:create, ALTER, DROP, truncate (table structure)2. Data manipulation statements: Dml:insert, delete, update, select3. Data Control statement: DCL: Authorization: GRANT, REVOKE permission: Revoke4. Error control statement: TCL: Start transaction: BEGIN TRANSACTION commit: Commit rollback: RollbackFour major integrity:1. Domain

Database Integrity refers to the correctness and compatibility of data in the Database. Database integrity is critical to the database application system and is reflected in many aspects. [Keyword] SQLServer Database Integrity refers to the correctness and compatibility of data in the Database. Database integrity is gu

I. The concept of integrity is introduced to avoid data corruption or inconsistency among multiple tables during data addition, deletion, and modification operations. Data Integrity means that the data stored in the database is correct and consistent. Ii. Integrity type four types of integrity constraints: domain

[PURPOSE] 1. Master the concept of integrity; 2. Familiar with SQL Server integrity technology. 3. Understand the integrity handling measures for SQL Server violations. [Lab nature] Comprehensive Experiment [Experiment Guide] 1Integrity Overview The correctness and compatibility of database integrity index data (lo

Integrity of the link model Integrity in the relational model refers to the correctness and consistency of data in the database. Data integrity is maintained by data integrity rules, including entity integrity rules and reference integri