使用 show-summary属性, :summary-method="自定义方法" 

<el-table v-loading="receiptLoading" :data="listInfo.Details" style="width: 100%" size="small" border show-summary :summary-method="getSummaries">
        <el-table-column prop="Quantity" :label="数量" />
		...
      </el-table>


	  // 明细表格自定义合计方法
const getSummaries = ({ columns, data }) => {
  const sums = [] as any[];
  columns.forEach((column, index) => {
    // 第一列显示"合计"
    if (index === 0) {
      sums[index] = '合计';
      return;
    }
    let array=["Quantity"]   //要求和的列
    // 判断是否是目标列
    if (array.includes(column.property)) {

      // 计算该列总和
      const values = data.map(item => new Decimal(item[column.property]));
      sums[index] = values.reduce((prev, curr) => prev.plus(new Decimal(curr.toString())), new Decimal(0));
    } else {
      // 其他列显示空
      sums[index] = '';
    }
  });
  return sums;
};