Question

我有一个相当简单的查询，它返回一个结果集，我不仅要进行分组和计数，还希望将结果转换为列名（在db2中）

    select t1.user,t2.category,t2.color,t2.store_number  
    from table1 t1
    inner join table2 t2 
    ON t1.store_number = t2.store_number;

返回：

    user | category  |  color  |  store_number
    --------------------------------------------
    12      A           'blue'      123             
    12      A           'blue'      123
    12      A           'blue'      456
    12      A           'blue'      456
    12      A           'blue'      456
    12      A           'blue'      123
    12      A           'blue'      123
    12      A           'blue'      456
    12      A           'blue'      123
    12      A           'blue'      789

从技术上讲，这将导致以下结果：

    user | store_number | count
    ------------------------------
    12        123           5
    12        456           4
    12        789           1

但是如何获取查询结果并将其实际转换为：

    user | 123  |  456  |  789
    ---------------------------
    12      5       4        1

因此，商店编号是列名，而计数是数据。我该怎么做呢？

Answer 1

我不认为DB2具有枢轴功能。您将需要使用案例语句和聚合。像这样：

import SwiftUI
import UIKit

struct ContentView: View {
    var body: some View {
        PageView([Color.red,Color.green,Color.yellow])
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}



struct PageViewController: UIViewControllerRepresentable {
    var controllers: [UIViewController]
    @Binding var currentPage: Int
    @Binding var progress : CGFloat

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    func makeUIViewController(context: Context) -> UIPageViewController {
        let pageViewController = UIPageViewController(
            transitionStyle: .scroll,
            navigationOrientation: .horizontal)
        pageViewController.dataSource = context.coordinator

        for view in pageViewController.view.subviews {
            if view is UIScrollView {
                (view as! UIScrollView).delegate = context.coordinator
            }
        }

        return pageViewController
    }

    func updateUIViewController(_ pageViewController: UIPageViewController, context: Context) {
        pageViewController.setViewControllers(
            [controllers[currentPage]], direction: .forward, animated: true)
    }

    class Coordinator: NSObject, UIPageViewControllerDataSource, UIPageViewControllerDelegate ,UIScrollViewDelegate {
        var parent: PageViewController

        init(_ pageViewController: PageViewController) {
            self.parent = pageViewController
        }

        func pageViewController(
            _ pageViewController: UIPageViewController,
            viewControllerBefore viewController: UIViewController) -> UIViewController?
        {
            guard let index = parent.controllers.firstIndex(of: viewController) else {
                return nil
            }
            if index == 0 {
                return parent.controllers.last
            }
            return parent.controllers[index - 1]
        }

        func pageViewController(
            _ pageViewController: UIPageViewController,
            viewControllerAfter viewController: UIViewController) -> UIViewController?
        {
            guard let index = parent.controllers.firstIndex(of: viewController) else {
                return nil
            }
            if index + 1 == parent.controllers.count {
                return parent.controllers.first
            }
            return parent.controllers[index + 1]
        }

        func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
            if completed,
                let visibleViewController = pageViewController.viewControllers?.first,
                let index = parent.controllers.firstIndex(of: visibleViewController)
            {
                parent.currentPage = index
            }
        }

        func scrollViewDidScroll(_ scrollView: UIScrollView) {
            let width = scrollView.frame.size.width
            let offsetX = scrollView.contentOffset.x
            let progress = (offsetX - width) / width
            self.parent.progress = progress
        }

    }
}




struct PageView<Page: View>: View {
    var viewControllers: [UIHostingController<Page>]
    @State var currentPage = 0
    @State var progress : CGFloat = 0

    init(_ views: [Page]) {
        self.viewControllers = views.map { UIHostingController(rootView: $0) }
    }

    var body: some View {
        VStack {
            PageViewController(controllers: viewControllers, currentPage: $currentPage,progress: $progress)
        }
    }
}

struct PageView_Previews: PreviewProvider {
    static var previews: some View {
        PageView([Color.red])
    }
}

db2，对数据进行分组，以便结果可以是列名

1 个答案: