ASP.NET adds data instance to database

USE [hovertree]
GO
/****** Object: Table [dbo].[hovertree_usermessage] ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[hovertree_usermessage](
[hvtId] [int] IDENTITY(1,1) NOT NULL,
[hvtTitle] [nvarchar](500) NULL,
[hvtContent] [nvarchar](max) NULL,
[hvtUser] [nvarchar](50) NULL,
[hvtTime] [datetime] NULL,
[hvtReply] [nvarchar](max) NULL,
[hvtIsShow] [bit] NULL,
CONSTRAINT [PK_hovertree_usermessage] PRIMARY KEY CLUSTERED 
(
[hvtId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[hovertree_usermessage] ADD CONSTRAINT [DF_hovertree_usermessage_hvtTime] DEFAULT (getdate()) FOR [hvtTime]
GO

string m_sql="insert into hovertree_usermessage (hvtTitle,hvtContent,hvtUser)values("  
+SQLTools.GetQuotes(txtTitle.Text)+","   
+ SQLTools.GetQuotes(txtContent.Text)+","   
+SQLTools.GetQuotes(txtUser.Text) +")";  
KeleyiSQLHelper.ExecuteSql(m_sql);