如何使用typescript从SQLite DB返回列的和？

下面是我的database.service.ts文件：

import { Injectable } from '@angular/core';
import { SQLite, SQLiteObject } from "@ionic-native/sqlite/ngx";
import { SQLitePorter } from "@ionic-native/sqlite-porter/ngx";
import { BehaviorSubject, Observable } from 'rxjs';
import { Platform } from '@ionic/angular';
import { HttpClient } from '@angular/common/http';


export interface scoVar {
  id: number,
  cLevel: number;
  levelScore: number,
  totalLevelScore: number,
  lStatus: string
}

@Injectable({
  providedIn: 'root'
})
export class DatabaseService {
  private database: SQLiteObject;
  private dbReady: BehaviorSubject<boolean> = new BehaviorSubject(false);

  scoInfo = new BehaviorSubject([]);


  constructor(private plt: Platform, private sqlitePorter: SQLitePorter, private sqlite: SQLite, private http: HttpClient) {
    this.plt.ready().then(() => {
      this.sqlite.create({
        name: 'scoInfo.db',
        location: 'default'
      })
        .then((db: SQLiteObject) => {
          this.database = db;
          this.seedDatabase();
        });
    });
  }

  seedDatabase() {
    this.http.get('assets/seed.sql', { responseType: 'text' })
      .subscribe(sql => {
        this.sqlitePorter.importSqlToDb(this.database, sql)
          .then(_ => {
            this.loadScoreTable();
            this.dbReady.next(true);
          })
          .catch(e => console.error(e));
      });
  }

  loadScoreTable() {
    return this.database.executeSql('SELECT * FROM scores', []).then(data => {
      let scoInfo: scoVar[] = [];

      if (data.rows.length > 0) {
        for (var i = 0; i < data.rows.length; i++) {
          scoInfo.push({
            id: data.rows.item(i).id,
            cLevel: data.rows.item(i).cLevel,
            levelScore: data.rows.item(i).levelScore,
            totalLevelScore: data.rows.item(i).totalLevelScore,
            lStatus: data.rows.item(i).lStatus
          });
        }
      }
      this.scoInfo.next(scoInfo);
    });
  }

  getDatabaseState() {
    return this.dbReady.asObservable();
  }

  getScos(): Observable<scoVar[]> {
    return this.scoInfo.asObservable();
  
  }
  
  getSum() {
    return this.database.executeSql('SELECT sum(levelScore) FROM scores').then(data => {
      return data;
    }).catch((e)=>{
      return "error on getting sum" + JSON.stringify(e);
    });
  }
}

下面是我的.html内容

<ion-header>
  <ion-toolbar color="primary">
    <ion-title>Dzo for Kids App</ion-title>
  </ion-toolbar>
</ion-header>

<ion-content>
  <div>
    <div>
      <ion-list *ngFor="let s of scoInfo">
        <ion-item>
          <h2>{{ s.id }}. {{ s.levelScore }}</h2>
          <p>{{ s.cLevel }}</p>
          <p>{{ s.totalLevelScore }}</p>
          <p>{{ s.lStatus }}</p>
        </ion-item>
      </ion-list>

     <ion-button expand="block" (click)="getLevelStatus()">Get Data</ion-button>
    </div>
  </div>

  <div>
      {{sum}}
  </div>

</ion-content>

根据我用来返回sum值的sql命令，“sum”的值应该是“14”。我没有得到[目标承诺]是什么，我为什么得到它？为什么我得不到总值？下面是我在sqlite db中的表格

0: {id: 1, cLevel: 1, levelScore: 5, totalLevelScore: 10, lStatus: "N/A"}
1: {id: 2, cLevel: 2, levelScore: 3, totalLevelScore: 10, lStatus: "N/A"}
2: {id: 3, cLevel: 3, levelScore: 2, totalLevelScore: 10, lStatus: "N/A"}
3: {id: 4, cLevel: 4, levelScore: 3, totalLevelScore: 10, lStatus: "N/A"}
4: {id: 5, cLevel: 5, levelScore: 1, totalLevelScore: 10, lStatus: "N/A"}

有人能帮我吗？我急需帮助。

带有Order By子句的SQLite SUM（）函数

从tablename[其中条件]中选择SUM（表达式） [表达分组]

> SELECT d.dept_name,SUM(e.salary) FROM emp_master e, dept_master d
> WHERE e.dept_id=d.dept_id GROUP BY e.dept_id;

0: {id: 1, cLevel: 1, levelScore: 5, totalLevelScore: 10, lStatus: "N/A"}
1: {id: 2, cLevel: 2, levelScore: 3, totalLevelScore: 10, lStatus: "N/A"}
2: {id: 3, cLevel: 3, levelScore: 2, totalLevelScore: 10, lStatus: "N/A"}
3: {id: 4, cLevel: 4, levelScore: 3, totalLevelScore: 10, lStatus: "N/A"}
4: {id: 5, cLevel: 5, levelScore: 1, totalLevelScore: 10, lStatus: "N/A"}

> SELECT d.dept_name,SUM(e.salary) FROM emp_master e, dept_master d
> WHERE e.dept_id=d.dept_id GROUP BY e.dept_id;