Mat-表头在两行，使用Angular 8

<mat-table [dataSource]="dataSource">
  <!-- 第一行表头 -->
  <ng-container matColumnDef="column1">
    <mat-header-cell *matHeaderCellDef>Column 1</mat-header-cell>
    <mat-cell *matCellDef="let element">{{element.column1}}</mat-cell>
  </ng-container>

  <!-- 第二行表头 -->
  <ng-container matColumnDef="column2">
    <mat-header-cell *matHeaderCellDef>Column 2</mat-header-cell>
    <mat-cell *matCellDef="let element">{{element.column2}}</mat-cell>
  </ng-container>

  <!-- 其他列定义... -->

  <!-- 表头行定义 -->
  <mat-header-row *matHeaderRowDef="['column1', 'column2', ...]"></mat-header-row>
  <mat-row *matRowDef="let row; columns: ['column1', 'column2', ...]"></mat-row>
</mat-table>

.mat-header-cell {
  display: flex;
  flex-direction: column;
  align-items: center;
}