我使用以下查询：
select a,b,c,d from Table1 where a in ('');
查询给出了如下输出：
a b c d
1 A 1e@c i-1
2 B #3ht i-2
3 A 1e@c Null
4 C 1e@c
现在我想对那些d为空或空白的记录应用 IF条件。
如果我找到与d值或b值对应的任何c值并在其他列e中显示，我想检查整个数据库。
期望的输出：
a b c d e
1 A 1e@c i-1
2 B #3ht i-2
3 A 1e@c Null i-1
4 C 1e@c i-1
答案 0 :(得分：3)
您可以将import { Component, OnInit, Input } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { AngularFireDatabase } from 'angularfire2/database';
import { AngularFirestore, AngularFirestoreCollection } from 'angularfire2/firestore';
import { Expense } from '../expenseModel';
@Component({
selector: 'app-view-expense',
templateUrl: './view-expense.component.html',
styleUrls: ['./view-expense.component.scss']
})
export class ViewExpenseComponent implements OnInit {
expenseId: any;
expensesCollection: AngularFirestoreCollection<Expense>;
expenses: Observable<Expense[]>;
expense: Observable<Expense>;
constructor(private db: AngularFirestore, private route: ActivatedRoute) {
this.route.params.subscribe(params => {
console.log(params);
this.expenseId = params.expenseId;
})
this.expensesCollection = this.db.collection('/expenses');
this.expenses = this.expensesCollection.snapshotChanges().map(changes = {
return changes.map(a => {
const data = a.payload.doc.data() as Expense;
data.id = a.payload.doc.id;
return data;
})
})
}
ngOnInit() {
this.getExpense();
}
getExpense() {
/* ---- ERROR HERE ---- */
this.expense = this.expensesCollection.where('expenseId', '==', this.expenseId);
console.log('this.expense: ' + this.expense);
}
}
表达式与相关子查询一起使用：
CASE如果您有多个匹配项，则可以使用SELECT t1.a, t1.b, t1.c, t1.d,
CASE
WHEN t1.d IS NULL OR t1.d = ''
THEN (SELECT t2.d
FROM Table1 AS t2
WHERE t2.c = t1.c LIMIT 1)
END AS e
FROm Table1 AS t1
WHERE t1.a IN (1, 2, 3, 4);
随意选择其中一个匹配项。否则使用一些谓词来选择所需的匹配记录。
答案 1 :(得分：0)
您可以使用SELECT IFNULL(d,'1-1') as e或SELECT IF((d = ''),'1-1','') as e或SELECT IF((d IS NULL) || (d = ''),'1-1','') as e
答案 2 :(得分：0)
试试这个：
@import '~angular-tree-component/dist/angular-tree-component.css';
答案 3 :(得分：0)
您可以使用CASE WHEN "Condition" THEN "do this"。
它基本上等同于SQL中的if语句。