using System.Data;

using System.Data.SqlClient;

using System.Configuration;

namespace WindowsFormsApp3

{

    public class DbHelper

    {

        private static string connStr = ConfigurationManager.ConnectionStrings["Demo"].ToString();

        /// <summary>

        /// 根据Sql语句返回Table类型数据

        /// </summary>

        /// <param name="sql">查询Sql语句</param>

        /// <returns>Table</returns>

        /// <SqlParameter>SqlParameter</SqlParameter>

        public static DataTable GetDataTable(string sql, SqlParameter[] sqlParameter = null)

        {

            DataSet ds = new DataSet();

            using (SqlConnection sqlConn = new SqlConnection(connStr))

            {

                sqlConn.Open();

                if (sqlConn.State == ConnectionState.Open)

                {

                    using (SqlCommand cmd = new SqlCommand(sql, sqlConn))

                    {

                        if (sqlParameter != null && sqlParameter.Length > )

                            cmd.Parameters.AddRange(sqlParameter);

                        SqlDataAdapter da = new SqlDataAdapter(cmd);

                        da.Fill(ds);

                    }

                }

            }

            return ds.Tables[];

        }

        /// <summary>

        /// 查询数据库是否存在数据

        /// </summary>

        /// <param name="sql">查询Sql语句</param>

        /// <param name="sqlParameter">查询参数</param>

        /// <returns>存在返回True，不存在返回False</returns>

        public static bool DataIsHasRows(string sql, SqlParameter[] sqlParameter = null)

        {

            bool HasRows = false;

            using (SqlConnection sqlConn = new SqlConnection(connStr))

            {

                sqlConn.Open();

                if (sqlConn.State == ConnectionState.Open)

                {

                    using (SqlCommand cmd = new SqlCommand(sql, sqlConn))

                    {

                        if (sqlParameter != null && sqlParameter.Length > )

                            cmd.Parameters.AddRange(sqlParameter);

                        using (SqlDataReader dr = cmd.ExecuteReader())

                        {

                            if (dr.HasRows)

                            {

                                HasRows = true;

                            }

                        }

                    }

                }

            }

            return HasRows;

        }

        /// <summary>

        /// 执行Sql语句返回受影响行数

        /// </summary>

        /// <param name="sql">Sql语句</param>

        /// <param name="sqlParameter">Sql参数</param>

        /// <returns>返回受影响行数</returns>

        public static int ExecNonQuery(string sql, SqlParameter[] sqlParameter =null)

        {

            int num = ;

            try

            {

                using (SqlConnection sqlConn = new SqlConnection(connStr))

                {

                    sqlConn.Open();

                    if (sqlConn.State == ConnectionState.Open)

                    {

                        using (SqlCommand cmd = new SqlCommand(sql, sqlConn))

                        {

                            if (sqlParameter != null && sqlParameter.Length > )

                                cmd.Parameters.AddRange(sqlParameter);

                            num = cmd.ExecuteNonQuery();

                        }

                    }

                }

                return num;

            }

            catch

            {

                return -;

            }

        }

        /// <summary>

        /// 返回第一行第一列内容

        /// </summary>

        /// <param name="sql"></param>

        /// <param name="sqlParameters"></param>

        /// <returns></returns>

        public static string ExecScalar(string sql, SqlParameter[] sqlParameter = null)

        {

            string value = "";

            using (SqlConnection sqlConn = new SqlConnection(connStr))

            {

                sqlConn.Open();

                if (sqlConn.State == ConnectionState.Open)

                {

                    using (SqlCommand cmd = new SqlCommand(sql, sqlConn))

                    {

                        if (sqlParameter != null && sqlParameter.Length > )

                            cmd.Parameters.AddRange(sqlParameter);

                        value = cmd.ExecuteScalar().ToString();

                    }

                }

            }

            return value;

        }

    }

}

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

    <startup>

        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />

    </startup>

  <connectionStrings>

    <add name="Demo" connectionString="Data Source=127.0.0.1;Initial Catalog=AdventureWorks;Persist Security Info=True;User ID=sa;Password=Sa123"/>

  </connectionStrings>

</configuration>