如果名称存在则更新否则插入 - 在 SQL Server 中

Question

如果给定的文件名已经在我的数据库中，我想在我的表中更新，否则我想插入一个新行。我尝试了这段代码，但EXISTS 显示的错误请给我正确的方法，因为我在 SQL 中更新鲜

public void SaveData(string filename, string jsonobject)
{
    SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=;Integrated Security=True");
    SqlCommand cmd;
    SqlCommand cmda;

    if EXISTS("SELECT * FROM T_Pages WHERE pagename = '" + filename + "") {
        cmda = new SqlCommand("UPDATE T_Pages SET pagename='" + filename + "',pageinfo='" + jsonobject + "' WHERE pagename='" + filename + "'", con);
        cmda.ExecuteNonQuery();
    }
    else {
        cmd = new SqlCommand("insert into T_Pages (pagename,pageinfo) values('" + filename + "','" + jsonobject + "')", con);
        cmd.ExecuteNonQuery();
    }

    con.Close();
}

Answer 1

你应该

• 在您的查询中使用 参数 - 总是！ - 没有例外
• 创建一个查询来处理服务器上的IF EXISTS() 部分
• 使用公认的 ADO.NET 最佳实践，将内容放入 using() {....} 块等中。

试试这个代码：

public void SaveData(string filename, string jsonobject)
{
    // define connection string and query
    string connectionString = "Data Source=.;Initial Catalog=;Integrated Security=True";
    string query = @"IF EXISTS(SELECT * FROM dbo.T_Pages WHERE pagename = @pagename)
                        UPDATE dbo.T_Pages 
                        SET pageinfo = @PageInfo
                        WHERE pagename = @pagename
                    ELSE
                        INSERT INTO dbo.T_Pages(PageName, PageInfo) VALUES(@PageName, @PageInfo);";

    // create connection and command in "using" blocks
    using (SqlConnection conn = new SqlConnection(connectionString))
    using (SqlCommand cmd = new SqlCommand(query, conn))
    {
        // define the parameters - not sure just how large those 
        // string lengths need to be - use whatever is defined in the
        // database table here!
        cmd.Parameters.Add("@PageName", SqlDbType.VarChar, 100).Value = filename;
        cmd.Parameters.Add("@PageInfo", SqlDbType.VarChar, 200).Value = jsonobject;

        // open connection, execute query, close connection
        conn.Open();
        int rowsAffected = cmd.ExecuteNonQuery();
        conn.Close();
    }
}

Answer 2

使用一个MERGE 语句怎么样？
当然用参数来避免SQL injection的风险。

public void SaveData(string filename, string jsonobject)
{
  SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=;Integrated Security=True");

  SqlCommand cmd;

  cmd = new SqlCommand(@"
    MERGE T_Pages AS target  
    USING (SELECT @PageName as pagename, @PageInfo as pageinfo) AS source 
    ON (target.pagename = source.pagename)  
    WHEN MATCHED THEN   
        UPDATE SET pageinfo = source.pageinfo  
    WHEN NOT MATCHED THEN  
    INSERT (pagename, pageinfo)  
    VALUES (source.pagename, source.pageinfo)", con);

   cmd.Parameters.Add(new SqlParameter("@PageName", filename));
   cmd.Parameters.Add(new SqlParameter("@PageInfo", jsonobject));

   con.Open();
   cmd.ExecuteNonQuery();
   con.Close();
 }

Answer 3

在数据库上创建存储过程

CREATE PROCEDURE T_Pages_Write  (@pagename nvarchar(256) ,@pageinfo nvarchar(max)) 
AS
IF EXISTS (SELECT pagename from T_Pages WHERE pagename = @pagename)
UPDATE T_Pages SET pageinfo = @pageinfo WHERE pagename = @pagename
ELSE 
INSERT T_Pages (pagename, Pageinfo) VALUES (@pagename, @Pageinfo)

然后从您的代码中调用它。你真的应该用参数化的命令来做到这一点（会有很多其他问题建议你最好的方法）。如果您愿意冒 SQL 注入攻击的风险，并且不介意在数据中有单引号字符时它会失败，那么您可以像这样快速而肮脏的方式来做到这一点

cmd = new SqlCommand("EXEC T_PagesWrite @pagename = '" + filename + "', @pageinfo ='" + jsonobject + "'", con);

Answer 4

public void SaveData(string filename, string jsonobject)
    {
        SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=;Integrated Security=True");
        SqlCommand cmd;
        SqlCommand cmda;

        SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM T_Pages WHERE pagename = '" + filename + "", con);
        DataSet ds = new DataSet();
        da.Fill(ds);



        if (ds.Tables[0].Rows.Count > 0)
        {

            cmda = new SqlCommand("UPDATE T_Pages SET pagename='" + filename + "',pageinfo='" + jsonobject + "' WHERE pagename='" + filename + "'", con);
            cmda.ExecuteNonQuery();
        }
        else
        {
            cmd = new SqlCommand("insert into T_Pages (pagename,pageinfo) values('" + filename + "','" + jsonobject + "')", con);
            cmd.ExecuteNonQuery();
        }


        con.Close();



    }

Answer 5

您可以通过一个查询来完成此操作

您要在哪里标记 int 类型的标志变量（您也可以将其设为 tinyint 类型，由您决定），如果计数为 0，则表示没有行，否则您更新查询

SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=;Integrated Security=True");
SqlCommand cmd;
cmda = new SqlCommand("declare @flag int ;set @flag = 0;select @flag = COUNT(*) FROM T_Pages WHERE pagename = '" + filename + "';IF @flag = 1 UPDATE T_Pages SET pagename='" + filename + "',pageinfo='" + jsonobject + "' WHERE pagename='" + filename + "';ELSE insert into T_Pages (pagename,pageinfo) values('" + filename + "','" + jsonobject + "');", con);
cmda.ExecuteNonQuery();
con.Close();