1、目标效果

        源码放在下面，复制粘贴即可

        （1）合计行放在头部，且字体颜色变粗、合计行背景色变粗

        （2）合计行年龄算平均值且字体颜色为绿色，财产算总数且字体颜色为红色 

2、原理

3、源码

        App.vue

<template>
  <div id="app">
    <SummaryTable></SummaryTable>
  </div>
</template>
 
<script>
import SummaryTable from '@/components/SummaryTable'
export default {
  components: {
    SummaryTable
  },
  name: 'App',
  data() {
    return {

    }
  },
}
</script>
 
<style>
#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

        SummaryTable.vue

<template>
    <div>
        <el-table ref="table" id="table" :data="tableData" border style="width: 100%" show-summary
            :summary-method="getSummaries">
            <el-table-column prop="date" label="日期" width="180" fixed="left">
            </el-table-column>
            <el-table-column prop="name" label="姓名" width="180" fixed="left">
            </el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="age" label="年龄"></el-table-column>
            <el-table-column prop="money" label="财产"></el-table-column>
            <el-table-column prop="money" label="财产"></el-table-column>
            <el-table-column prop="money" label="财产"></el-table-column>
            <el-table-column prop="money" label="财产"></el-table-column>
        </el-table>
    </div>
</template>
   
<script>

export default {
    name: 'App',
    data() {
        return {
            tableData: [{
                date: '2016-05-01',
                name: '王小虎',
                age: 13,
                money: 100
            }, {
                date: '2016-05-02',
                name: '王小虎',
                age: 25,
                money: 333
            }, {
                date: '2016-05-03',
                name: '王小虎',
                age: 33,
                money: 555
            }, {
                date: '2016-05-04',
                name: '王小虎',
                age: 23,
                money: 200
            },
            {
                date: '2016-05-05',
                name: '王小虎',
                age: 26,
                money: 666
            }],
        }
    },
    watch: {
        tableData: {
            immediate: true,
            handler() {
                setTimeout(() => {
                    const tds = document.querySelectorAll('#table .el-table__fixed-footer-wrapper tr>td');
                    tds[0].colSpan = 2;
                    tds[0].style.textAlign = 'center'
                    tds[1].style.display = 'none'
                }, 0)
            }
        }
    },
    methods: {
        // 合计行方法
        getSummaries(param) {
            const { columns, data } = param;
            const sums = [];
            columns.forEach((column, index) => {
                if (column.property == 'date') {
                    sums[index] = '总价';
                    return;
                }

                // values是每一列的数据是一个数组
                const values = data.map(item => Number(item[column.property]));
                if (!values.every(value => isNaN(value))) {
                    // 对values进行一个累加操作，累加那些非NAN的值
                    const total = values.reduce((prev, curr) => {
                        const value = Number(curr);
                        if (!isNaN(value)) {
                            return prev + curr;
                        } else {
                            return prev;
                        }
                    }, 0);

                    // 年龄计算平均值（绿色）
                    if (column.property == 'age') {
                        sums[index] = <span class={'green'}>{total / data.length}</span>
                    }

                    // 财产计算总数（红色）
                    if (column.property == 'money') {
                        sums[index] = <span class={'red'}>{total}</span>
                    }

                }
            });
            // 将合计结果返回，是一个数组，每个位置的值与表格的列一一对应
            return sums
        }
    }
}
</script>
   
<style scoped>
.red {
    color: red;
    font-weight: bolder;
}

.green {
    color: lightgreen;
    font-weight: bolder;
}

/* 存在固定列时，合计行位置修改开始 */
.el-table /deep/ .el-table__fixed {
    display: flex;
    flex-direction: column;
}

.el-table /deep/ .el-table__fixed-footer-wrapper,
.el-table /deep/ .el-table__fixed-body-wrapper,
.el-table /deep/ .el-table__fixed-header-wrapper {
    position: initial;
}

.el-table /deep/ .el-table__fixed-body-wrapper {
    order: 1;
}

.el-table /deep/ .el-table__fixed-footer-wrapper tbody td.el-table__cell {
    border-top: none;
    background: black;
    color: white;
    font-weight: bolder;
}

/* 存在固定列时，合计行位置修改开始 */

/* 默认有1px去掉样式影响 */
.el-table /deep/ .el-table__fixed::before {
    height: 0;
}

/* 合计行整体样式修改开始 */
.el-table /deep/ .el-table__footer-wrapper tbody td {
    background: black;
    color: white;
    font-weight: bolder;
}

/* 合计行整体样式修改结束*/


/* 合计行位置修改开始 */
.el-table {
    display: flex;
    flex-direction: column;
}

.el-table /deep/ .el-table__body-wrapper {
    order: 1;
}

/* 合计行位置修改结束*/
</style>