合并场景：如果id一样，则主表列合并，子表列不做合并，可实现单行、多行合并，亲测！！！
展示效果如图示：

组件代码：

// table组件  :span-method="objectSpanMethod" 一定要有这个方法，合并逻辑都在这个里面
	<el-table
			:data="dataList"
			:span-method="objectSpanMethod"
			border
		>
			<el-table-column prop="className" label="班级" />
			<el-table-column prop="name" label="姓名" />
			<el-table-column prop="sex" label="性别"  />
			<el-table-column prop="dataType" label="科目" />
			<el-table-column prop="score" label="分数" />
		</el-table>

js代码：

//数据格式
dataList: [
				{id:"1",className:"3-1",name:"张三",sex:"男",dataType:"数学",score:"81"},
				{id:"1",className:"3-1",name:"张三",sex:"男",dataType:"英语",score:"33"},
				{id:"1",className:"3-1",name:"张三",sex:"男",dataType:"历史",score:"66"},
				{id:"2",className:"3-2",name:"李四",sex:"女",dataType:"科学",score:"13"},
				{id:"2",className:"3-2",name:"李四",sex:"女",dataType:"英语",score:"90"},
			],

//合并的js逻辑  需要合并多少列就写几列
objectSpanMethod({row, column, rowIndex, columnIndex}) {
			const _row = this.flitterData(this.dataList).one[rowIndex];
			const _col = _row > 0 ? 1 : 0;
			//合并第一列
			if (columnIndex === 0) {
				return {
					rowspan: _row,
					colspan: _col,
				};
			}
			//合并第二列
			if (columnIndex === 1) {
				return {
					rowspan: _row,
					colspan: _col,
				};
			}
			//合并第三列
			if (columnIndex === 2) {
				return {
					rowspan: _row,
					colspan: _col,
				};
			}
		},
		flitterData(arr) {
			let spanOneArr = [];
			let concatOne = 0;
			arr.forEach((item, index) => {
				if (index === 0) {
					spanOneArr.push(1);
				} else {
					// 如果id一样，就合并，根据自己的需求来改，id换为要比较的列名
					if (item.id == arr[index - 1].id) {
						spanOneArr[concatOne] += 1;
						spanOneArr.push(0);
					} else {
						spanOneArr.push(1);
						concatOne = index;
					}
				}
			});
			return {
				one: spanOneArr,
			};
		},