el-table 排序

在项目中使用el-table的默认排序功能产生问题，如按照数字排序，当数字有多位时，只按照第一位数字排序问题，
问题复现：

添加代码修改：
主要是这一行sort-method，传递的item.prop就是el-table-column 中的prop字段

:sort-method="(a, b) => sortMethod(item.prop, a, b)"

<el-table :data="tableData" style="width: 100%;background:transparent;" :height="tableMaxHeight"
				:header-cell-style='headerCellStyle' :header-row-style='headerRowStyle' :row-style='rowStyle'
				:cell-style="rowCellStyle" class="dealljtable projecttable tableindexstyle"
				@cell-mouse-enter="handlerTableOver" @cell-mouse-leave="handlerTableOut" >
				<el-table-column label="" type="index" width="60">
				</el-table-column>
				<el-table-column :min-width="item.width || 80" v-for="item in headerKeys" :key="item.label"
					align="center" :fixed="item.fixed" :prop="item.prop" :minWidth="item.minWidth"
					:sortable="item.label === '成交套数' ? true : false"
					:sort-method="(a, b) => sortMethod(item.prop, a, b)"
					:sort-orders="['ascending', 'descending']">
					<template slot="header">
						<div class="header-wrap">
							<span class="label">{{ item.label }}</span>
							<div class="unit" v-if="item.unit">({{ item.unit }})</div>
						</div>
					</template>
					<template slot-scope="scope">
						<div class="handle-icon palterow" v-if="scope.column.property === 'caption'">
							{{ scope.row[scope.column.property] != null ? scope.row[scope.column.property] : '-' }}---

						</div>
						<div v-else class="handle-icon">
							{{ scope.row[scope.column.property] != null ? scope.row[scope.column.property] : '-' }}
						</div>

					</template>
				</el-table-column>
				<template slot="empty">
					<NoData></NoData>
				</template>
			</el-table>

data(){
	return{
		headerKeys: [
				{
					label: '项目名称',
					key: '',
					unit: '',
					prop: "caption",
					minWidth: '100',
				},
				{
					label: '建筑年代',
					key: '',
					unit: '',
					prop: "buildingYear",
					minWidth: '80',
				},
				{
					label: '成交套数',
					key: '',
					unit: '套',
					prop: "tradeCount",
					minWidth: '90',
					sortable: true,
				},
				{
					label: '成交均价',
					key: '',
					unit: '元/m²',
					prop: "tradePrice",
					minWidth: '100',
				}, {
					label: '成交金额',
					key: '',
					unit: '万元',
					prop: "tradeMoney",
					minWidth: '100',
				},

			],
	}
}			
methods: {
//sortMethod方法
		sortMethod(key, a, b) {
			let _a = a[key] ?? 0;
			let _b = b[key] ?? 0;
			return _a - _b;
		},		
}