Tài liệu Adding Tables to a Database pdf

[ Team LiB ]Recipe 10.8 Adding Tables to a Database Problem You need to add a table to an existing database.. Solution Use the CREATE TABLE statement.. The sample code executes the DD

[ Team LiB ]

Recipe 10.8 Adding Tables to a Database

Problem

You need to add a table to an existing database

Solution

Use the CREATE TABLE statement

The sample code executes the DDL statement—using the ExecuteNonQuery( ) method of the Command object—to add a table to an existing SQL Server database

The C# code is shown in Example 10-8

Example 10-8 File: AddTableToDatabaseForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

//

SqlConnection conn = new SqlConnection(

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

String createSql = "CREATE TABLE MyTable " +

"(MyTableId int IDENTITY(1,1) PRIMARY KEY CLUSTERED)";

SqlCommand cmd = new SqlCommand(createSql, conn);

// Create the table in the database

try

{

conn.Open( );

cmd.ExecuteNonQuery( );

resultTextBox.Text = "Table created successfully";

}

catch (System.Exception ex)

{

resultTextBox.Text = ex.ToString( );

}

finally

{

if (conn.State == ConnectionState.Open)

conn.Close( );

}

Discussion

There are two categories of SQL statements:

Database Definition Language (DDL)

Used to manage all objects in the database, generally with CREATE, ALTER, and DROP statements to create, modify, and delete objects, respectively These

statements generally require DBA permissions to execute

Database Management Language (DML)

Used to manipulate—select, insert, update, and delete—data in the database

objects Database objects are defined using DDL

The solution executes a DDL CREATE TABLE statement to create a table in the

database and a primary key on the new table in a SQL Server database

You can programmatically drop a table using the DROP TABLE statement in a similar way To drop the table created in this example, use the following code:

DROP TABLE MyTable

The DROP TABLE statement will fail if the table is in use; therefore, it might be

necessary to restart the SQL Server

For more information about the CREATE TABLE statement or the DROP TABLE

statement, see Microsoft SQL Server Books Online

The solution for Oracle databases and other databases is similar to that shown for SQL Server However, the DDL syntax for each database varies slightly because of differences

in database server capabilities and architecture For example, the CREATE TABLE statement for Oracle is different because Oracle does not support identity columns and uses sequences instead (see Recipe 4.4 for more information about Oracle sequences) For more information about Oracle SQL syntax, see Oracle in a Nutshell by Rick

Greenwald and David C Kreines (O'Reilly)

[ Team LiB ]