ExecuteNonQuery(),ExecuteScalar(),ExecuteReader的用法
2010-04-19 20:51
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using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{ conn.Open(); SqlCommand cmd = new SqlCommand("SELECT * FROM Person.Address", conn); SqlDataReader reader = cmd.ExecuteReader(); while(reader.Read()) Console.WriteLine(reader["AddressLine1"]);}catch(SqlException ex){ Console.WriteLine(ex.Message);}finally{ conn.Close();}
[1] ExecuteNonQuery 方法用法：ExecuteNonQuery方法用来执行INSERT、UPDATE、DELETE和其他没有返回值得SQL命令，——比如CREATE DATABASE 和 CREATE TABLE 命令。当使用 INSERT、UPDATE、DELETE时，ExecuteNonQuery返回被命令影响的行数。对所有其他命令，返回-1。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.open();==============================================================-- INSERT 命令SqlCommand cmd = new SqlCommand("INSERT INTO titles(title_id, title, type, pubdate) " + "VALUES('JP101', 'Programming Microsoft .NET', 'bussiness', 'May 2002')", conn);==============================================================-- UPDATE 命令-- SqlCommand cmd = new SqlCommand("UPDATE titles SET title_id= 'JP2002' " + -- "WHERE title_id = 'JP1001'", conn);==============================================================-- DALETE 命令-- SqlCommand cmd = new SqlCommand("DELETE FROM titles WHERE title_id = 'JP202'", conn);==============================================================cmd.ExecuteNonQuery();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{conn.Close();}
[2] ExecuteScalar 方法用法1：ExecuteScalar 方法执行一个SQL命令返回结果集的第一列的第一行。它经常用来执行SQL的COUNT、AVG、MIN、MAX 和 SUM 函数，这些函数都是返回单行单列的结果集。''注意：''ExecuteScalar 一般返回一个Object类型，因此必须把它转换为强类型。如果转换不正确，.NET框架就会引发 InvalidCastException异常。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("SELECT MAX(advance) FROM titles", conn);decimal amount = (decimal) cmd.ExecuteScalar();Console.WriteLine("ExecuteScalar returned {0:c}", amount);}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{conn.Close();}用法2.1：ExecuteScalar 方法的另一个普遍的用法是从数据库中检索BLOB(二进制大对象)。下面的例子从Pubs数据库的Pub_Info表的Logo字段中检索图像，并把他封装到一个位图中。MemoryStream stream = new MemoryStream();SqlConnection conn = new SqlConnection("server=ws7\leosql;database=pubs;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("SELECT logo FROM pub_info WHERE pub_id='0736'", conn);byte[] blob = (byte[]) cmd.ExecuteScalar();stream.Write(blob, 0, blob.Length);Bitmap bitmap = new Bitmap(stream);// TODO：使用位图bitmap.Dispose();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{stream.Close();conn.Close();}
用法2.2：您也许对如何把BLOB写入数据库感兴趣，答案是在包装了INSERT命令(该命令中包含了类型为byte[]的输入参数)的命令对象上调用ExcuteNonQuery方法。下面例子在Pubs数据库的Pub_Info表中插入一条记录，记录的Logo字段包含一个BLOB。-- 定义和初始化blob变量FileStream stream = new FileStream("Logo.jpg", FileMode.Open);byte[] blob = new byte[stream.Length];stream.Read(blob, 0, (int) stream.Length);stream.Close();
SqlConnection conn = new SqlConnection("server=ws7\leosql;database=pubs;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("INSERT INTO pub_info(pub_id, logo) VALUES('9937', @logo)", conn);cmd.Parameters.Add("@logo", blob);cmd.ExecuteNonQuery();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{stream.Close();conn.Close();}
[3] ExecuteReader 方法用法：ExecuteReader 方法存在的目的只有一个：尽可能快地对数据库进行查询并得到结果。ExecuteReader 返回一个DataReader对象：如果在SqlCommand对象中调用，则返回SqlDataReader；如果在OleDbCommand对象中调用，返回的是OleDbDataReader。可以调用DataReader的方法和属性迭代处理结果集。它是一个快速枚举数据库查询结果的机制，是只读、只进的。对SqlDataReader.Read的每次调用都会从结果集中返回一行。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.Open();SqlCommand cmd = new SqlCommand("SELECT * FROM titles", conn);SqlDataReader reader = cmd.ExecuteReader();while(reader.Read()) Console.WriteLine(reader["title"]); ================================= -- Console.WriteLine(reader.GetName(0)); =================================}catch(SqlException ex){Console.WriteLine(ex.Message);}finally{conn.Close();}
DataReader还有一个GetValue方法可以用来检索字段的值。GetValue返回一个一般性的Object，但是被无数个返回强类型的Get方法补充，比如GetInt32和GetDecimal（参考MSDN2005）。对GetOrdinal的调用是必须的，因为GetDecimal只接受整型索引。GetOrdinal所做的工作正好与GetName相反——它把字段名转换成数字索引。注意：DataReader必须处理Close方法。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.Open();SqlCommand cmd = new SqlCommand("SELECT * FROM titles WHERE advance != 0", conn);SqlDataReader reader = cmd.ExecuteReader();int index = reader.GetOrdinal("advance");while(reader.Read()) Console.WriteLine("{0:c}", reader.GetDecimal(index)); ================================= -- Console.WriteLine(reader.GetName(0)); =================================''reader.Close();''}catch(SqlException ex){Console.WriteLine(ex.Message);}finally{========================================================-- 可以配置DataReader，使它真的可以关闭一个底层连接-- reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);========================================================conn.Close();
[1] ExecuteNonQuery 方法用法：ExecuteNonQuery方法用来执行INSERT、UPDATE、DELETE和其他没有返回值得SQL命令，——比如CREATE DATABASE 和 CREATE TABLE 命令。当使用 INSERT、UPDATE、DELETE时，ExecuteNonQuery返回被命令影响的行数。对所有其他命令，返回-1。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.open();==============================================================-- INSERT 命令SqlCommand cmd = new SqlCommand("INSERT INTO titles(title_id, title, type, pubdate) " + "VALUES('JP101', 'Programming Microsoft .NET', 'bussiness', 'May 2002')", conn);==============================================================-- UPDATE 命令-- SqlCommand cmd = new SqlCommand("UPDATE titles SET title_id= 'JP2002' " + -- "WHERE title_id = 'JP1001'", conn);==============================================================-- DALETE 命令-- SqlCommand cmd = new SqlCommand("DELETE FROM titles WHERE title_id = 'JP202'", conn);==============================================================cmd.ExecuteNonQuery();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{conn.Close();}
[2] ExecuteScalar 方法用法1：ExecuteScalar 方法执行一个SQL命令返回结果集的第一列的第一行。它经常用来执行SQL的COUNT、AVG、MIN、MAX 和 SUM 函数，这些函数都是返回单行单列的结果集。''注意：''ExecuteScalar 一般返回一个Object类型，因此必须把它转换为强类型。如果转换不正确，.NET框架就会引发 InvalidCastException异常。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("SELECT MAX(advance) FROM titles", conn);decimal amount = (decimal) cmd.ExecuteScalar();Console.WriteLine("ExecuteScalar returned {0:c}", amount);}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{conn.Close();}用法2.1：ExecuteScalar 方法的另一个普遍的用法是从数据库中检索BLOB(二进制大对象)。下面的例子从Pubs数据库的Pub_Info表的Logo字段中检索图像，并把他封装到一个位图中。MemoryStream stream = new MemoryStream();SqlConnection conn = new SqlConnection("server=ws7\leosql;database=pubs;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("SELECT logo FROM pub_info WHERE pub_id='0736'", conn);byte[] blob = (byte[]) cmd.ExecuteScalar();stream.Write(blob, 0, blob.Length);Bitmap bitmap = new Bitmap(stream);// TODO：使用位图bitmap.Dispose();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{stream.Close();conn.Close();}
用法2.2：您也许对如何把BLOB写入数据库感兴趣，答案是在包装了INSERT命令(该命令中包含了类型为byte[]的输入参数)的命令对象上调用ExcuteNonQuery方法。下面例子在Pubs数据库的Pub_Info表中插入一条记录，记录的Logo字段包含一个BLOB。-- 定义和初始化blob变量FileStream stream = new FileStream("Logo.jpg", FileMode.Open);byte[] blob = new byte[stream.Length];stream.Read(blob, 0, (int) stream.Length);stream.Close();
SqlConnection conn = new SqlConnection("server=ws7\leosql;database=pubs;uid=sa;pwd=lixiang@");try{conn.open();SqlCommand cmd = new SqlCommand("INSERT INTO pub_info(pub_id, logo) VALUES('9937', @logo)", conn);cmd.Parameters.Add("@logo", blob);cmd.ExecuteNonQuery();}catch(SqlException ex){Console.WriteLine(ex.Message); }finally{stream.Close();conn.Close();}
[3] ExecuteReader 方法用法：ExecuteReader 方法存在的目的只有一个：尽可能快地对数据库进行查询并得到结果。ExecuteReader 返回一个DataReader对象：如果在SqlCommand对象中调用，则返回SqlDataReader；如果在OleDbCommand对象中调用，返回的是OleDbDataReader。可以调用DataReader的方法和属性迭代处理结果集。它是一个快速枚举数据库查询结果的机制，是只读、只进的。对SqlDataReader.Read的每次调用都会从结果集中返回一行。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.Open();SqlCommand cmd = new SqlCommand("SELECT * FROM titles", conn);SqlDataReader reader = cmd.ExecuteReader();while(reader.Read()) Console.WriteLine(reader["title"]); ================================= -- Console.WriteLine(reader.GetName(0)); =================================}catch(SqlException ex){Console.WriteLine(ex.Message);}finally{conn.Close();}
DataReader还有一个GetValue方法可以用来检索字段的值。GetValue返回一个一般性的Object，但是被无数个返回强类型的Get方法补充，比如GetInt32和GetDecimal（参考MSDN2005）。对GetOrdinal的调用是必须的，因为GetDecimal只接受整型索引。GetOrdinal所做的工作正好与GetName相反——它把字段名转换成数字索引。注意：DataReader必须处理Close方法。using System.Data.SqlClient;...SqlConnection conn = new SqlConnection(@"server=ws7\leosql;database=AdventureWorks;uid=sa;pwd=lixiang@");try{conn.Open();SqlCommand cmd = new SqlCommand("SELECT * FROM titles WHERE advance != 0", conn);SqlDataReader reader = cmd.ExecuteReader();int index = reader.GetOrdinal("advance");while(reader.Read()) Console.WriteLine("{0:c}", reader.GetDecimal(index)); ================================= -- Console.WriteLine(reader.GetName(0)); =================================''reader.Close();''}catch(SqlException ex){Console.WriteLine(ex.Message);}finally{========================================================-- 可以配置DataReader，使它真的可以关闭一个底层连接-- reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);========================================================conn.Close();
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