C# 对int字段的查询找到行，对char字段的查询不找到行，c oledb

使用C和OleDB连接到Access数据库

我有三个几乎相同的查询字符串：

"select * from stock_head where sh_id = 19;"
"select * from stock_head where sh_lineno = 32059";
"select * from stock_head where sh_ref='#007705';";

第一个和第二个检索行，每种情况下的字段都是整数，最后一个不是整数，它是字符字段，并且行确实存在：

ExecuteQuery - select * from stock_head where sh_lineno = 32059
ID 7705, #007705, 32059, NS, 'NO SALE', 04/02/2017 14:29:00
1 row(s) found

ExecuteQuery - select * from stock_head where sh_ref='#007705';
0 row(s) found

通过C和OleDB查询字符字段有什么奇怪的地方吗？我试着用“like”代替“=”，用单引号和双引号来分隔值，但都没有用

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.Linq;

namespace OleDbTest
{
class Program
{
    static void Main( string[] args )
    {
        // Create Profile File object
        ProcessEJFile EJP = new ProcessEJFile(
            "Provider=Microsoft.ACE.OLEDB.12.0;" +
            @"Data Source=E:\Users\sallyw\Documents\Bar.accdb;" +
            "Persist Security Info=False;");

        //// Get last reference from the Stock Header file
        //object retVal = EJP.ExecuteScalar(
        //    @"SELECT max(stock_head.[sh_ref]) FROM stock_head where sh_ref like ""[#]%"";", null);
        //string maxRef = retVal.ToString();
        //Console.WriteLine( "maxRef = {0}", maxRef );

        // Get the actual row
        string query =
             // @"select * from stock_head where sh_ref = '{0}';";
             //"select * from stock_head where sh_id = 19;";
             "select * from stock_head where sh_lineno = 32059";

        List<StockHead> shlist = EJP.GetStockHead(query, null );
        if ( shlist == null )
        {
            Console.WriteLine( "shlist is null" );
        }
        else
        {
            foreach (StockHead sh in shlist )
            {
                Console.WriteLine( sh.ToString() );
            }
            Console.WriteLine( "{0} row(s) found", shlist.Count());
        }

        query =
             // @"select * from stock_head where sh_ref = '{0}';";
             "select * from stock_head where sh_ref='#007705';";

        List<StockHead> shlist1 = EJP.GetStockHead(query, null );
        if ( shlist1 == null )
        {
            Console.WriteLine( "shlist1 is null" );
        }
        else
        {
            foreach ( StockHead sh in shlist1 )
            {
                Console.WriteLine( sh.ToString() );
            }
            Console.WriteLine( "{0} row(s) found", shlist1.Count() );
        }
        Console.ReadLine();
    }
}

class ProcessEJFile
{
    AccessDatabase Accdb = null;

    public ProcessEJFile( string connectionString )
    {
        Accdb = new AccessDatabase( connectionString );
    }

    public List<StockHead> GetStockHead( string sql, params object[] args )
    {
        DataTable t;

        Accdb.ExecuteQuery( out t, sql, args );

        if ( t != null )
        {
            List<StockHead> shlist = new List<StockHead>();

            foreach ( DataRow r in t.Rows )
            {
                StockHead sh = new StockHead( r);
                shlist.Add( sh );
            }
            return shlist;
        }
        else
        {
            return null;
        }
    }

    // Get a single value - MAX, COUNT etc.
    public Object ExecuteScalar( string sql, params object[] args )
    {
        return Accdb.ExecuteScalar( sql, args );
    }
}


class AccessDatabase
{
    public OleDbConnection conn = new OleDbConnection();

    public AccessDatabase( string connection )
    {
        conn.ConnectionString = connection;
    }

    public bool OpenDatabase()
    {
        try
        {
            conn.Open();
        }
        catch ( Exception ex )
        {
            return false;
        }
        return true;
    }

    public void CloseDatabase()
    {
        if ( conn == null )
            return;

        conn.Close();
    }

    public void ExecuteQuery( out DataTable dataTable, string sql, params object[] args )
    {
        dataTable = new DataTable();
        string query;

        // Simplified version not validating or cleaning arguments in any way
        if ( args == null )
        {
            query = sql;
        }
        else
        {
            query = string.Format( sql, args );
        }

        Console.WriteLine( "\nExecuteQuery - {0}", query );

        if ( OpenDatabase() )
        {
            OleDbCommand command = new OleDbCommand( query, conn );
            OleDbDataAdapter adapter = new OleDbDataAdapter( command );
            adapter.Fill( dataTable );
        }
    }

    public object ExecuteScalar( string sql, params object[] args )
    {
        Object returnValue = null;
        string query = sql;

        if ( OpenDatabase() )
        {
            OleDbCommand cmd = new OleDbCommand( query, (OleDbConnection)conn);
            returnValue = cmd.ExecuteScalar();
        }
        return returnValue;
    }
}

class StockHead
{
    public int sh_id;
    public string sh_ref;
    public int sh_lineno = 0;
    public string sh_type;
    public string sh_supplier = "";
    public DateTime sh_datetime;

    public StockHead( DataRow row )
    {
        this.sh_id = (int)row[ "sh_id" ];
        this.sh_ref = (string)row[ "sh_ref" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_lineno = (int)row[ "sh_lineno" ];
        }
        this.sh_type = (string)row[ "sh_type" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_supplier = (string)row[ "sh_supplier" ];
        }
        this.sh_datetime = (DateTime)row[ "sh_datetime" ];
    }

    public override string ToString()
    {
        return String.Format( "ID {0}, {1}, {2}, {3}, '{4}', {5}",
                this.sh_id, this.sh_ref, this.sh_lineno, this.sh_type, this.sh_supplier, this.sh_datetime );
    }
}

---

}`您的查询没有问题。这是失败的，因为您每次执行查询时都试图通过调用ExecuteQuery中的OpenDatabase来打开与数据库的连接。第二次OpenDatabase失败，因为数据库已打开，并且查询未执行

您正在捕获错误，但未对其执行任何操作。给出的信息是

The connection was not closed. The connection's current state is open.

这可以通过单步执行代码轻松找到。您没有在调试中运行它吗

你可以把它改成

public bool OpenDatabase()
{
    try
    {
        if (conn.State != ConnectionState.Open)
        {
            conn.Open();
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
        return false;
    }
    return true;
}

---

如果捕捉到错误，则对其进行处理，而不是返回False

sh_ref列的确切类型是什么？您可以在Access中运行该查询，然后它是否工作？如果没有，你可能会有一个隐藏的字符困扰你。是的，它在access中运行良好。它是一个短文本。谢谢，我以为会很简单。我该怎么做？看不到明显的链接，但我的代码中的明显内容逃过了我的眼睛…在您单击的答案旁边有一个复选标记。看啊，淡灰色的蜱虫。勾选它。谢谢