使用金额(总).SQL语句在PHP+MySQL中工作良好

我试图在我的Visual Studio 2015 c#项目中重用一些mySQL。我试图从数据库中检索输出，其中总结了每个销售人员的销售和总销售量。当在我的PHP项目中使用mySQL语句时，我得到了错误:

The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

代理结构:

CREATE TABLE [dbo].[AGENT] (
    [AgentID]   INT  IDENTITY (1, 1) NOT NULL,
    [AgentName] TEXT NOT NULL,
    [OfficeKey] INT  NOT NULL,
    PRIMARY KEY CLUSTERED ([AgentID] ASC)
);

办公室结构:

CREATE TABLE [dbo].[OFFICE] (
    [OfficeID]       INT        IDENTITY (1, 1) NOT NULL,
    [OfficeLocation] NCHAR (20) NOT NULL,
    PRIMARY KEY CLUSTERED ([OfficeID] ASC)
);

销售结构:

CREATE TABLE [dbo].[SALE] (
    [SaleID]         INT             IDENTITY (1, 1) NOT NULL,
    [SaleDate]       DATE            NOT NULL,
    [AgentKey]       INT             NOT NULL,
    [Amount]         MONEY           NOT NULL,
    [DestinationKey] INT             NOT NULL,
    PRIMARY KEY CLUSTERED ([SaleID] ASC)
);

来源:

namespace Desktop_Campus_Travel
{
    public partial class Agent_Bookings : Form
    {
        public Agent_Bookings()
        {
            InitializeComponent();
        }
        private void Agent_Bookings_Load(object sender, EventArgs e)
        {
            List<AgentBooking> agentList = new List<AgentBooking>();
            SqlConnection conn = Database.GetConnection();
            string selStmt = @"
SELECT AGENT.AgentName, 
       OFFICE.OfficeLocation,
       COUNT(AGENT.AgentID) AS Sales,
       SUM(SALE.Amount) AS Total 
FROM   AGENT 
       JOIN OFFICE 
         ON AGENT.OfficeKey = OFFICE.OfficeID 
       JOIN SALE 
         ON SALE.AgentKey = AGENT.AgentID 
GROUP  BY AGENT.AgentName";
            SqlCommand selCmd = new SqlCommand(selStmt, conn);
            try
            {
                conn.Open();
                SqlDataReader reader = selCmd.ExecuteReader();
                while (reader.Read())
                {
                    AgentBooking agent = new AgentBooking();
                    agent.AgentName = reader["AgentName"].ToString();
                    agent.OfficeLocation = reader["OfficeLocation"].ToString();
                    agent.Sales = reader["Sales"].ToString();
                    agent.Total = reader["Total"].ToString();
                    agentList.Add(agent);
                }
                reader.Close();
            }
            catch (SqlException ex) { throw ex; }
            finally { conn.Close(); }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}

CREATE TABLE [dbo].[AGENT] (
    [AgentID]   INT  IDENTITY (1, 1) NOT NULL,
    [AgentName] NVARCHAR(100) NOT NULL,
    [OfficeKey] INT  NOT NULL,
    PRIMARY KEY CLUSTERED ([AgentID] ASC)
);

SELECT
    AGENT.AgentName, 
    OFFICE.OfficeLocation,
    SALE2.Sales,
    SALE2.Total
FROM 
    AGENT 
    JOIN OFFICE ON AGENT.OfficeKey = OFFICE.OfficeID 
    JOIN
    (
        SELECT 
            SALE.AgentKey,
            COUNT(SALE.SaleID) AS Sales,
            SUM(SALE.Amount) AS Total 
        FROM   SALE 
        GROUP  BY SALE.AgentKey
    ) SALE2 ON SALE2.AgentKey = AGENT.AgentID