C # database Query summary

First, create a SQL Server database as a test database, create a table and fill in the test data

Database: SQL Server

Database name: Blog

Table Name: Test

Note: The database connection can use "dbl" file test, the specific use of Baidu can be.

1. Query all data from the database to DataGridView

Statement: SELECT * from Test

1   Private voidButton1_Click (Objectsender, EventArgs e)2  {3       stringConnStr ="Data source=long-pc\\long;initial Catalog=blog; User Id=long; Password=longtao";4       stringCmdstr="SELECT * from Test";5             6SqlConnection conn =NewSqlConnection (CONNSTR);7 Conn. Open ();8 9SqlCommand cmd =NewSqlCommand ();TenCmd.commandtext =Cmdstr; OneCmd. Connection =Conn; ASqlDataAdapter adap =NewSqlDataAdapter (cmd); -DataSet ds =NewDataSet (); - ADAP. Fill (DS); theDatagridview1.datasource = ds. tables[0]. DefaultView; -}

2. Query the database for some data and display it to DataGridView

Statement: String cmdstr = "Select Name, age from Test";

1  Private voidButton2_Click (Objectsender, EventArgs e)2  {3      stringConnStr ="Data source=long-pc\\long;initial Catalog=blog; User Id=long; Password=longtao";4      stringCmdstr ="select name, age from Test";5 6SqlConnection conn =NewSqlConnection (CONNSTR);7 Conn. Open ();8 9SqlCommand cmd =NewSqlCommand ();TenCmd.commandtext =Cmdstr; OneCmd. Connection =Conn; ASqlDataAdapter adap =NewSqlDataAdapter (cmd); -DataSet ds =NewDataSet (); - ADAP. Fill (DS); theDatagridview1.datasource = ds. tables[0]. DefaultView; -}

3. Displaying data using column aliases

Statement: String cmdstr = "SELECT name as name, age as aged from Test";

Note: In the statement "as" keyword, you can use a space instead

1   Private voidButton3_Click (Objectsender, EventArgs e)2   {3       stringConnStr ="Data source=long-pc\\long;initial Catalog=blog; User Id=long; Password=longtao";4       stringCmdstr ="select name as name, age as the from Test";5 6SqlConnection conn =NewSqlConnection (CONNSTR);7 Conn. Open ();8 9SqlCommand cmd =NewSqlCommand ();TenCmd.commandtext =Cmdstr; OneCmd. Connection =Conn; ASqlDataAdapter adap =NewSqlDataAdapter (cmd); -DataSet ds =NewDataSet (); - ADAP. Fill (DS); theDatagridview1.datasource = ds. tables[0]. DefaultView; -}

4. Using column calculations

Statement: String cmdstr = "Select name, age, language, math, English, Chinese + math + English as total score from Test";

1   Private voidButton4_Click (Objectsender, EventArgs e)2   {3      stringConnStr ="Data source=long-pc\\long;initial Catalog=blog; User Id=long; Password=longtao";4      stringCmdstr ="select name, age, language, math, English, Chinese + math + English as total score from Test";5 6SqlConnection conn =NewSqlConnection (CONNSTR);7 Conn. Open ();8 9SqlCommand cmd =NewSqlCommand ();TenCmd.commandtext =Cmdstr; OneCmd. Connection =Conn; ASqlDataAdapter adap =NewSqlDataAdapter (cmd); -DataSet ds =NewDataSet (); - ADAP. Fill (DS); theDatagridview1.datasource = ds. tables[0]. DefaultView; -}

5. Limit query Value range size

Statement: String cmdstr = "Select name, age, language, math, English, Chinese + math + English as total score from Test where (language + math + English) >215";

1   Private voidButton5_click (Objectsender, EventArgs e)2   {3       stringConnStr ="Data source=long-pc\\long;initial Catalog=blog; User Id=long; Password=longtao";4       stringCmdstr ="select name, age, language, math, English, Chinese + math + English as total score from Test where (language + math + English) >215";5 6SqlConnection conn =NewSqlConnection (CONNSTR);7 Conn. Open ();8 9SqlCommand cmd =NewSqlCommand ();TenCmd.commandtext =Cmdstr; OneCmd. Connection =Conn; ASqlDataAdapter adap =NewSqlDataAdapter (cmd); -DataSet ds =NewDataSet (); - ADAP. Fill (DS); theDatagridview1.datasource = ds. tables[0]. DefaultView; -}

C # database Query summary