C# 去除DataTable表中重复行

https://blog.csdn.net/weixin_41561640/article/details/106133842

去除DataTable表中重复行有两种方法：
一、利用sql语句的distinct 关键字
如：select distinct * from table_name;
二、利用DataView.ToTable()方法
1.DataView.ToTable()

根据现有DataView中的行，创建并返回一个新的DataTable。

2.DataView.ToTable(String)

根据现有DataView中的行，创建并返回一个新的DataTable。参数String为返回的DataTable的名称，输出的表与输入表的列相通，不可自定义。

3.DataView.ToTable(Boolean,String[])

根据现有DataView中的行，创建并返回一个新的DataTable。参数Boolean如果为true，则去重，为false时不去重，且默认为false。

可自定义返回的列，数组String[]为显示返回列的集合。

例子：

//去掉重复行
DataTable dt = db.GetDataTable("select * from 表名"); //获得datatable
DataView dv = dt.DefaultView;
table = dv.ToTable(true, new string[] { "name", "code" });


public DataTable GetDataTable(string strSql)

{

try

{

//DataSet dataSet = new DataSet();

//SqlDataAdapter adapter = new SqlDataAdapter(strSql, _Connection);

//adapter.Fill(dataSet);

//return dataSet.Tables[0]; 

DataTable dt= new DataTable ();

SqlDataAdapter adapter = new SqlDataAdapter(strSql, _Connection);

adapter.Fill(dt);

return dt;

}

catch

{

return null;

}

}


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如果有一组数据（id不是唯一字段）

name	code
张三	123
李四	123
张三	456
张三	123

通过上面的方法得到

name	code
张三	123
李四	123
张三	456

4.DataView.ToTable(String,Boolean,String[])

根据现有DataView中的行，创建并返回一个新的DataTable。第一个参数string用来定义返回表的名称。

注意：想要的结果是只针对其中的一列去重，还要显示其他的列，怎么做

#region 删除DataTable重复列，类似distinct
        /// <summary>   
        /// 删除DataTable重复列，类似distinct   
        /// </summary>   
        /// <param name="dt">DataTable</param>   
        /// <param name="Field">字段名</param>   
        /// <returns></returns>   
        public static DataTable DeleteSameRow(DataTable dt, string Field)
        {
            ArrayList indexList = new ArrayList();
            // 找出待删除的行索引   
            for (int i = 0; i < dt.Rows.Count - 1; i++)
            {
                if (!IsContain(indexList, i))
                {
                    for (int j = i + 1; j < dt.Rows.Count; j++)
                    {
                        if (dt.Rows[i][Field].ToString() == dt.Rows[j][Field].ToString())
                        {
                            indexList.Add(j);
                        }
                    }
                }
            }
            indexList.Sort();
 // 排序
            for (int i = indexList.Count - 1; i >= 0; i--)// 根据待删除索引列表删除行  
            {
                int index = Convert.ToInt32(indexList[i]);
                dt.Rows.RemoveAt(index);
            }
            return dt;
        }

    <span class="token comment">/// &lt;summary&gt;   </span>
    <span class="token comment">/// 判断数组中是否存在   </span>
    <span class="token comment">/// &lt;/summary&gt;   </span>
    <span class="token comment">/// &lt;param name="indexList"&gt;数组&lt;/param&gt;   </span>
    <span class="token comment">/// &lt;param name="index"&gt;索引&lt;/param&gt;   </span>
    <span class="token comment">/// &lt;returns&gt;&lt;/returns&gt;   </span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">bool</span> <span class="token function">IsContain</span><span class="token punctuation">(</span><span class="token class-name">ArrayList</span> indexList<span class="token punctuation">,</span> <span class="token keyword">int</span> index<span class="token punctuation">)</span>
    <span class="token punctuation">{<!-- --></span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> indexList<span class="token punctuation">.</span>Count<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span>
        <span class="token punctuation">{<!-- --></span>
            <span class="token keyword">int</span> tempIndex <span class="token operator">=</span> Convert<span class="token punctuation">.</span><span class="token function">ToInt32</span><span class="token punctuation">(</span>indexList<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>tempIndex <span class="token operator">==</span> index<span class="token punctuation">)</span>
            <span class="token punctuation">{<!-- --></span>
                <span class="token keyword">return</span> <span class="token keyword">true</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> <span class="token keyword">false</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token preprocessor property">#<span class="token directive keyword">endregion</span></span>


    <span class="token comment">/// &lt;summary&gt;   </span>
    <span class="token comment">/// 判断数组中是否存在   </span>
    <span class="token comment">/// &lt;/summary&gt;   </span>
    <span class="token comment">/// &lt;param name="indexList"&gt;数组&lt;/param&gt;   </span>
    <span class="token comment">/// &lt;param name="index"&gt;索引&lt;/param&gt;   </span>
    <span class="token comment">/// &lt;returns&gt;&lt;/returns&gt;   </span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">bool</span> <span class="token function">IsContain</span><span class="token punctuation">(</span><span class="token class-name">ArrayList</span> indexList<span class="token punctuation">,</span> <span class="token keyword">int</span> index<span class="token punctuation">)</span>
    <span class="token punctuation">{<!-- --></span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> indexList<span class="token punctuation">.</span>Count<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span>
        <span class="token punctuation">{<!-- --></span>
            <span class="token keyword">int</span> tempIndex <span class="token operator">=</span> Convert<span class="token punctuation">.</span><span class="token function">ToInt32</span><span class="token punctuation">(</span>indexList<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span>tempIndex <span class="token operator">==</span> index<span class="token punctuation">)</span>
            <span class="token punctuation">{<!-- --></span>
                <span class="token keyword">return</span> <span class="token keyword">true</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> <span class="token keyword">false</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token preprocessor property">#<span class="token directive keyword">endregion</span></span>

借鉴文章：
1、C# DataTable去重，根据列名去重保留其他列
原文链接：https://blog.csdn.net/qq_23502409/article/details/75269221
2、C# 中怎样去除DataTable表里面的重复行
原文链接：https://blog.csdn.net/u010892197/article/details/50310907
3、c# DataView.ToTable() 方法 去除表中的重复项
原文链接：https://blog.csdn.net/JYL15732624861/article/details/61422332

---

注意：
比如：
DataTable dt=db.GetDataTable(“select * from 表名”); //获得datatable
DataView dv = new DataView(dt);//对dt这个表创建一个视图（注意：这里的DataView只能对一个datatable进行创建视图）
DataTable dt2 = dv.ToTable(true, “name“,”age“,”sex”);//true:true 去除重复，false 不去除; "name“,“age”,“sex”:表示需要显示的字段,特别注意：需要将每个栏位用双引号括起来，不然会报错：列“name,age,sex”不属于基础表
————————————————
原文链接：https://blog.csdn.net/qq_27929003/article/details/105675240