Database knowledge that .net programmers need to know

About the database

As a "feeling" (higher B) .NET development engineer, I need to know some little stories like this.

Even if it’s just as some nonsense talk.

1. File database (common)

Access

SQLite

SQLServerCE

2. There are two types of SQLServer

To be precise, when it comes to SQLServer, there are actually two types, namely MSSQLServer and SyBaseSQLServer.

The relationship between the two is like this.

SQL Server is a relational database management system (DBMS) developed and promoted by Microsoft. It was originally jointly developed by Microsoft, Sybase and Ashton-Tate, but later as the cooperation between the two companies ended, they separately developed their own Different extensions have been added to the version.

So there are

MSSQLServer,

and SyBaseSQLServer.

3. Batch process startup How to use batch process to start the SqlServer service?

Start: net start mssqlserver (service name)

Close: net stop mssqlserver (service name)

Note: Windows 7 or above versions need to run cmd as administrator.

4. Login failure Solution to login failure

1) Log in using Windows authentication method and see if the verification method is supported!

2) Log in using Windows authentication, [Security] → [Login Name] to see if it is disabled!

5. Primary Key What types of primary keys include?

Business primary key is similar to student number, employee number, ID card number, etc. Generally, university courses will use this kind of thing as the primary key by default! (Not recommended)

Logical primary key has no practical meaning, it is just a number and has nothing to do with business logic. (Recommendation)

Combined primary key Two fields together serve as the primary key! This is often done in college courses. But (strongly not recommended)

6. Data types Commonly used data types in MSSqlServer

1) Image

2) String

char(10) varchar(10) nchar(10) nvarchar(10)

varchar(max) nvarchar(max) text(10) ntext(10)

2.1) The difference between char and varchar

char char It is of fixed length

It is of variable length From the perspective of compressed space , it is generally better to use varchar.

2.2) The difference between nchar and char

0 letters, 10 Chinese character.

2.3) What type of storage is used for long text?以Server 2000 before using Text / NTEXT