elementui如何合并单元格，并且赋值索引，加上序号

<template>
  <div class="">
    <el-table
        :data="listData"
        :span-method="objectSpanMethod"
        class="tableArea"
        style="width: 100%">
        <el-table-column
          prop="type"
          label="序号"
          align="center"
          width="200"/>
        <el-table-column
          prop="sheetType"
          label="工单类型"
          />
        <el-table-column
          prop="taskKey"
          label="taskKey"
          />
        <el-table-column
          prop="templateUrl"
          label="templateUrl"
          />
        <el-table-column
          label="操作"
          >
          <template slot-scope="scope">
          	<el-tooltip class="item" effect="dark" content="修改" placement="top-start">
				      <i class="el-icon-edit-outline"  @click="modify(scope)" />
				    </el-tooltip>
				    <el-tooltip class="item" effect="dark" content="删除" placement="top-start">
            <i class="el-icon-delete" @click="deleteData(scope)" />
				    </el-tooltip>
          </template>
        </el-table-column >
      </el-table>