A Simple Problem with Integrity Constraints for SQL 10

There is no date type, only datetime, which you can use varchar(10) instead.

As you operate, the string in the date format will be converted to the date format.

For example, if you store a string in your database: "2006-1-3", you can treat it as a date-based field.

2.Use the decimal type:

For example, the field name decimal(3,1).

That is, accurate to the last decimal place, there are four significant digits.

1. Entity integrity: Each row of the table is the only entity in the table.

2. Domain completeness: It means that the columns in the table must meet the constraints of a specific data reference type, and the constraints include the value range, accuracy, etc.

3. Referential integrity: It means that the data of the main keywords and external keywords of the two tables should be consistent, which ensures the consistency of the data between the tables and prevents data loss or the spread of meaningless data in the database.

4. User-defined integrity: Different relational database systems often require some special constraints depending on their application environment. User-defined integrity is a constraint for a particular relational database that reflects the semantic requirements that must be met for a particular application.

Relational bai

Integrity constraints typically include domain integrity, DU entity integrity, ZHI

Referential integrity and user-defined DAO integrity roundability.

1. Domain integrity is the simplest and most basic constraint to ensure the rationality of the value of the database answer field.

2. Physical integrity, which refers to ensuring that information or data is not tampered with without authorization or can be quickly discovered after tampering in the process of transmitting and storing information or data.

3. Referential integrity, which is used to define the constraints of the main keyword and the external keyword reference to establish the connection between the relationship. Relational databases often contain multiple relationships that are interconnected, and relationships are connected through common attributes.

4. The user-defined integrity function is to put forward binding conditions for the data involved in a specific application according to the requirements of the application environment and the actual needs.

SQL constraints are divided into entity integrity, referential integrity, user-defined integrity, and deletion constraints.

Physical integrity.

1.When you create a table, you define the primary key.

create table table name.

sno int identity(1,1),sname nvarchar(20),- Set the primary key.

primary key (sno)

2.Add a primary key.

alter table name.

Add constraint pk table name sno

primary key(id)

Referential integrity.

1.A foreign key is defined when you create a table.

create table table name.

sno int identity(1,1) primary key,cno int not null,foreign key(cno) references

Table name 2 (CNO).

on delete cascade -- cascade delete.

on update cascade -- cascade updates.

on delete on action.

2.Add a foreign key.

alter table name.

add constraint fk table name Table name 2

foreign key(cid) references Table name2(cid).

User-defined integrity.

Non-null constraints. alter table name.

alter column name varchar(20) not null

2.Unique constraints.

alter table name.

add constraint uq table name Column name unique (column).

3.Check the constraints.

alter table name.

add constraint ck table name Column name check(age>5).

4.Default constraints.

alter table name.

add constraint df table name column name default('Male')

for gender

Delete Constraint -- Deletes the constraint.

alter table name drop constraint df table name column.

—Physical integrity.

Copyability: Also known as row integrity, it requires that there cannot be identical rows in the table, and each row must have a non-empty and non-repeating primary key value.

Referential integrity: Also known as referential integrity, it refers to the rules between tables that act on two or more related tables to make the key values in the table consistent in the related tables by using the relationship between the primary key and the foreign key (or unique key).

User-defined integrity: Refers to the constraints of a specific relational database that reflect the semantic requirements that must be met by the data involved in a specific application.

Primary key constraints.

Foreign key constraints. Attribute value constraints.

There are three integrity constraints for databases: entity integrity, referential integrity, and user-defined integrity.

Here's a more detailed explanation.

The integrity of the data is achieved by adding constraints. The methods for implementing integrity constraints vary from category to category. Integrity constraints can be divided into two broad categories: static constraints and dynamic constraints.

1. Static constraints.

Static constraints are constraints on the state of the database, which can be divided into fixed constraints, implicit constraints, and display constraints.

2. Support.

are constraints inherent in the data model, such as the properties of the relationship are atomic, i.e., the constraints that satisfy the inf. Intrinsic constraints are taken into account when implementing the DBMS.

3. Implicit constraints.

Refers to constraints implicit in a data schema, typically described in Data Definition Language (DDL) statements, and stored in a data catalog. For example, domain integrity constraints, entity integrity, and referential integrity constraints are all described by the corresponding DDL statements.

4. Display constraints.

Inherent constraints and implicit constraints are the most basic constraints, but they cannot summarize all constraints. Data integrity is diverse, and depends on the semantics and application of data, and these constraints are only explicitly stated, so they are called explicit constraints. There are generally three ways to explain explicit constraints:

Explain constraints with procedures. This approach does not contain the description and validation of the application to the application, where you can insert procedures to verify that a database update violates a given constraint, and if the constraint is violated, to roll back the transaction. The process of testing constraints is generally written in a general-purpose high-level programming language, which can express a wide variety of constraints.

This is a universal approach.

Explain constraints in language. An assertion is a logical condition that must be met for the state of a database. A database integrity constraint can be thought of as a collection of assertions. In order to represent constraints, the DBMS must provide an assertion description language.

Constraints are represented by triggers. A trigger is a software mechanism that functions like wheneverthen, i.e., once a given condition is true, the system initiates the corresponding action. Triggers can be used to represent constraints, with constraint violation as a condition and constraint violation processing as an action.

Actions are not limited to rolling back a transaction, but can also give the user a message or procedure. Once a batch of triggers is defined in the system, the database state is monitored, and if there is an update that violates the constraints, the corresponding action is triggered.

5. Dynamic constraints.

Dynamic constraints are not constraints on the state of the database, but constraints that should be observed when the database changes from one state to another, for example, when updating the employee table, the values of attributes such as wages and years of service generally only increase, not decrease. Dynamic constraints are also generally explicitly stated.

Among the above constraints, inherent constraints are necessarily enforced, implicit constraints are basically or partially implemented in most modern DBMS, and explicit and dynamic constraints are only implemented in individual DBMS.

All data values stored in the database are in the correct state.