Question

我正在寻找一种方法，使用Swift中的FMDB从7个不同的表中打印出四个特定的列。我尝试用点符号选择它们，但这似乎不起作用。

DB看起来像这样：

艺术家：[ArtistId]，[姓名]
追踪：[TrackId]，[AlbumId]，[Name]
专辑：[AlbumId]，[Name]，[ArtistId]
类型：[GenreId]，[姓名]
发票：[CustomerId]，[InvoiceId]
InvoiceLine：[InvoiceId]
客户：[CustomerId]，[FirstName]，[LastName]，[City]

import Foundation

let database = FMDatabase(path: " /path to database.sqlite/ ")

database.open()

let rs = try database.executeQuery("SELECT Artist.Name, Track.Name, Album.Title, Genre.Name 
                                    FROM Invoice, Customer, InvoiceLine, Track, Album, Artist, Genre
                                    WHERE Customer.FirstName = 'Michelle'
                                    AND Customer.LastName = 'Brooks' 
                                    AND Customer.City = 'New York'
                                    AND Invoice.CustomerId=Customer.CustomerId 
                                    AND InvoiceLine.InvoiceId = Invoice.InvoiceId 
                                    AND Track.TrackId = InvoiceLine.TrackId 
                                    AND Album.AlbumId = Track.AlbumId 
                                    AND Artist.ArtistId = Album.ArtistId
                                    AND Genre.GenreId = Track.GenreId ", values: nil)

while rs.next() {
    let artistName = rs.stringForColumn("Artist.Name")
    let trackName = rs.stringForColumn("Track.Name")
    let albumTitle = rs.stringForColumn("Album.Title")
    let genre = rs.stringForColumn("Genre.Name")

print (artistName + " " + trackName + " " + albumTitle + " " + genre)
}

Answer 1

问题是stringForColumn（使用sqlite_column_name）函数正在使用基础表的列名，而忽略了表的名称。更糟糕的是，如果您有两个相同名称的列，则无法知道您希望从哪个表中获得结果。

所以，有两种解决方法：

您可以为列添加唯一名称：

let rs = try database.executeQuery("SELECT Artist.Name AS ArtistName, Track.Name AS TrackName, Album.Title, Genre.Name AS Genre.Name ..."

然后

let artistName = rs.stringForColumn("ArtistName")
let trackName = rs.stringForColumn("TrackName")
let albumTitle = rs.stringForColumn("Title")
let genre = rs.stringForColumn("GenreName")

或

使用列号：

let artistName = rs.stringForColumnIndex(0)
let trackName = rs.stringForColumnIndex(1)
let albumTitle = rs.stringForColumnIndex(2)
let genre = rs.stringForColumnIndex(3)

在Swift中使用FMDB从多个表中进行选择

1 个答案: