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string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";

//LAPTOP-82MUPKTO       The name of the connected database server 
//CSDN Give me peace of mind A3 The database of     Database name of the connection

Database server with account and password login （sqlserver Identity Authentication ） Write it like this

 string connStr = "Data Source= Server name ;Initial Catalog= Database name ;User ID =  account number ;Password= password ";

Pass the connection parameter string into the database link class , Generate linked objects conn

SqlConnection conn = new SqlConnection(connStr);
//SqlConnection  Variable name  = new SqlConnection( Parameter strings or variables that store parameter strings );

Test the link , The link succeeds without any error

conn.Open();// Open database link , The later you drive, the better 
conn.Close();// Close database links , Turn it off when you're done , Don't hang on

The necessary preparations have been made OK 了

Let's talk about sql Statement writing and execution .

SQL Statement writing and execution

To write

Let's define a string Type of sql Variables to store our sql sentence ,sql The statement only needs the original syntax , No need to change .

sqlserver This is the general way to create a data table in

Here we turn him into one line , Never mind indenting .

string sql = "create table csdn A data sheet to give me peace of mind 1(name varchar(8) not null)";

Someone will ask. , my sql The content of the statement should change continuously , But the format is basically the same . You can't write another one . Actually, it's not that much trouble , use C# Of String.Format() Generate sql Just a statement string .

C# in string.format usage C# in string.format Usage details (IT technology )

For example, the name of the data table I want to create should be replaced , Let's add a placeholder to the table name OK

string tablename="csdn A data sheet to give me peace of mind 1";// I'm the name of the watch 
string sql = String.Format("create table {0}(name varchar(8) not null)", tablename);
//tablename The contents of the string will replace the {0}, therefore sql The content of will follow tablename Change by change

perform

Create actuator

sql We have written the sentence , Then it will be executed

We call SqlCommand Class generates a sql Statement executors cmd, Pass in sql Statements and linked variables

SqlCommand cmd = new SqlCommand(sql, conn);
// Format :    SqlCommand  Custom actuator variable name = new SqlCommand(sql String variable ,  Link variables );

We have created the actuator , Next, select the execution method , Different execution methods have different return values .

Special reminder ： Remember to open the link before using

conn.Open();

ExecuteNonQuery() How to execute

cmd.ExecuteNonQuery();

ExecuteScalar() How to execute

cmd.ExecuteScalar();

Difference between the two

ExecuteReader() How to execute

cmd.ExecuteReader();

The function of this execution method will be explained in detail in the following examples

Special reminder ： Please close the connection after execution

 conn.Close();

example ：

1- Create a data table

Create a personal transcript for Xiao Ming

Want to use sql Statement to create a data table

create table  Table name 
(
     Name   data type   Is it allowed to be empty (null||not null),
     Name 2  data type   Is it allowed to be empty (null||not null),
     Name 3  data type   Is it allowed to be empty (null||not null),
        ……
     Name n  data type    Is it allowed to be empty (null||not null)
)

C# Code

    using System.Data.SqlClient;// Don't forget , If the header is added, it shows that it has not been called , Please check Nuget package 

    public static void addtable(string tablename)
    {
        // Test connection database 
        string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";
        SqlConnection conn = new SqlConnection(connStr);
        // Open database 
        conn.Open();

        // To write sql sentence , Grammar is sql grammar 
        string sql = String.Format("create table {0}( Course name  varchar(11) not null, achievement   tinyint     not null)", tablename);
        SqlCommand cmd = new SqlCommand(sql, conn);
        // Intimate , Exception handling is arranged 
        try
        {
            cmd.ExecuteNonQuery();
            Console.WriteLine(" Data table created successfully ");
        }
        catch (SqlException ae)
        {
            Console.WriteLine(" Data table creation failed ");
            Console.WriteLine(ae.Message);
        }
        finally
        {
            conn.Close();// After the database operation is completed , Need to close database , Free memory 
        }

    }

    
    addtable(" Test results ")

Wuhu takes off

2- Insert data into table

Xiao Ming passed his computer science exam 100 branch , Help him record it

Want to use sql Insert data instructions in

insert into  Table name 
values
(' data 1',' data 2',' data 3')// The first line of data , There are only a few columns in the table structure , Where it is allowed to be empty, you can just type ''
(' data 1',' data 2',' data 3')// The second row of data , There are only a few columns in the table structure , Where it is allowed to be empty, you can just type ''

    public static void adddata(string classname,int grade)
    {
        // Test connection database 
        string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";
        SqlConnection conn = new SqlConnection(connStr);
        // Open database 
        conn.Open();

        // To write sql sentence , Grammar is sql grammar 
        string sql = String.Format("insert into  Test results  values('{0}','{1}')",classname,grade);
        SqlCommand cmd = new SqlCommand(sql, conn);
        try
        {
            cmd.ExecuteNonQuery();
            Console.WriteLine(" Score entered successfully ");
        }
        catch (SqlException ae)
        {
            Console.WriteLine(" Score entry failed ");
            Console.WriteLine(ae.Message);
        }
        finally
        {
            conn.Close();// After the database operation is completed , Need to close database , Free memory 
        }
    }



data_Control.adddata(" Computer science ",100);

3- Modify the data in the table

I went to , Xiao Ming was found cheating in the exam , achievement 0 branch , Help him change

update  Table name 
set  Name 1=' value ', Name 2=' value ' where  filter

    public static void changedata(string classname,int new_grade)
    {
        // Test connection database 
        string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";
        SqlConnection conn = new SqlConnection(connStr);
        // Open database 
        conn.Open();

        // To write sql sentence , Grammar is sql grammar 
        string sql = String.Format("update  Test results  set  achievement ='{0}' where  Course name ='{1}'", new_grade,classname);
        SqlCommand cmd = new SqlCommand(sql, conn);
        try
        {
            cmd.ExecuteNonQuery();
            Console.WriteLine(" Score modified successfully ");
        }
        catch (SqlException ae)
        {
            Console.WriteLine(" Grade modification failed ");
            Console.WriteLine(ae.Message);
        }
        finally
        {
            conn.Close();// After the database operation is completed , Need to close database , Free memory 
        }
    }

changedata(" Computer science ",0);

4- Delete data in table

Xiao Ming is afraid of being fried with shredded pork with bamboo shoots by his father , Give me a 1 Bao La bribed me to delete this record , I'm sure I won't help him just for a bag of spicy sticks

, But he took 2 The bag is another matter .

delete from  Table name  where  filter

    public static void delete_data(string classname)
    {
        // Test connection database 
        string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";
        SqlConnection conn = new SqlConnection(connStr);
        // Open database 
        conn.Open();

        // To write sql sentence , Grammar is sql grammar 
        string sql = String.Format("delete from  Test results  where  Course name ='{0}'", classname);
        SqlCommand cmd = new SqlCommand(sql, conn);
        try
        {
            cmd.ExecuteNonQuery();
            Console.WriteLine(" Results deleted successfully ");
        }
        catch (SqlException ae)
        {
            Console.WriteLine(" Failed to delete grade ");
            Console.WriteLine(ae.Message);
        }
        finally
        {
            conn.Close();// After the database operation is completed , Need to close database , Free memory 
        }
    }

delete_data(" Computer science ");

Xiao Ming goes home happily , As soon as he left, I wrote back my grades ……

5- Read data from table

The school will print out Xiao Ming's report card .

ExecuteReader() Here comes the usage of , Thank you for seeing here .

The usage is in the following code

select * from  Test results

    public static void get_data()
    {
        // Test connection database 
        string connStr = "Data Source=LAPTOP-82MUPKTO;Initial Catalog=CSDN Give me peace of mind A3 The database of ;Integrated Security=True";
        SqlConnection conn = new SqlConnection(connStr);
        // Open database 
        conn.Open();

        // To write sql sentence , Grammar is sql grammar 
        string sql = String.Format("select * from  Test results ");
        SqlCommand cmd = new SqlCommand(sql, conn);

        SqlDataReader rdr = cmd.ExecuteReader();// Define data readers rdr Get the returned data 
        while (rdr.Read())// Once at a time Read(), Read a row of data from the data 
        {
            string classname=rdr[" Course name "].ToString();// By column name , Get the course name information in this line , because rdr[" Course name "] The return is object type , So we need to carry out type conversion , The following is the same principle 
            int grade = Convert.ToInt32(rdr[" achievement "]);// By column name , Get the score information in the line 
            Console.WriteLine(" Course name :{0}, achievement :{1}",classname,grade);
        }
        conn.Close();// Always ensure that the database is open when reading 

    }