el-table 多级表头固定列问题

当我们的表格有两个或者多个一级表头时，若想固定，那么就必须要给“一级标表头”这一列的宽度=包含的列宽总和。比如下面的三个姓名列，每列是150，一级标表头的宽度就是450

<template>
  <el-table
    :data="tableData"
    height="350"
    style="width: 100%">
    <el-table-column
      type="index"
      label="序号"
      width="60"
      fixed>
    </el-table-column>
    
      <el-table-column
        label="一级标题1"
        align="center"
        width="450"
        fixed>
        
        <el-table-column 
        prop="name"
        label="姓名111"
        width="150">
        </el-table-column>
        
        <el-table-column 
        prop="name"
        label="姓名222"
        width="150">
        </el-table-column>
        
        <el-table-column 
        prop="name"
        label="姓名333"
        width="150">
        </el-table-column>
      </el-table-column>
      
    <el-table-column label="一级标题2" width="120"     align="center">
      <el-table-column
        prop="date"
        label="日期"
        width="120">
      </el-table-column>
      <el-table-column label="地址">
        <el-table-column
          prop="province"
          label="省份"
          width="120">
        </el-table-column>
        <el-table-column
          prop="city"
          label="市区"
          width="120">
        </el-table-column>
        <el-table-column
          prop="address"
          label="地址"
          width="300">
        </el-table-column>
        <el-table-column
          prop="address"
          label="地址"
          width="300">
        </el-table-column><el-table-column
          prop="address"
          label="地址"
          width="300">
        </el-table-column>
        <el-table-column
          prop="address"
          label="地址"
          width="300">
        </el-table-column>
        <el-table-column
          prop="zip"
          label="邮编"
          width="120">
        </el-table-column>
      </el-table-column>
    </el-table-column>
  </el-table>
</template>