Question

如何获得获取树子的步骤数。

例如我有一个这样的表：

id    title      parent_id
1       A           0
2       B           0
3       C           1
4       F           3
5       O           3
6       D           2
7       J           6
8       T           2
9       P           8


A   // 1 step
   C   //2 step
      F   //3 step
      O   //3 step

B   //1 step
  D  //2 step
    J  //3 step
  T  //2 step
    P  //3 step

例如，如果我给出一个像1（id = 1）的数字，它应该返回1而id = 6它应该返回2作为步骤。

我的DBMS是MySQL。

Answer 1

如果您的树不是很深，它可以是一个递归存储过程。像这样的东西（加上适当的条件处理程序），或任何类似的东西，它可以用各种方式编写：

class = "dynamicSI"

此外，MariaDB 10.2支持递归CTE。它现在是一个早期的测试版，所以它不适合制作，但如果你只评估你的选择，你可以尝试一下。这应该有效：

library(ggplot2)
library(shiny)

server <- function(input, output, session) {

  R = mtcars[,c("cyl","am","carb","gear")]

  output$FILTERS = renderUI({
    selectInput("filters","Filters",choices = names(R),multiple = TRUE)
  })

  observe({

    req(input$filters)
    filter_names = input$filters

    # count how many filters I selected
    n = length(filter_names)     

    # to render n selectInput    
    lapply(1:n,function(x){
      output[[paste0("FILTER_",x)]] = renderUI({
        req(input$filters)
        div( class = "dynamicSI",
          selectInput(paste0("filter_",x),
                      paste0(filter_names[x]),
                      choices = unique(R[,filter_names[x]]),
                      multiple = TRUE,
                      selected = unique(R[,filter_names[x]])
                      ),
          actionButton(paste0("filter_all_",x),"(Un)Select All", 
                       data = paste0("filter_",x), # selectInput id
                       name = paste0(filter_names[x])) # name of column
        )
      })
    })

    output$FILTER_GROUP = renderUI({
      div(class="dynamicSI",
        lapply(1:n, function(i){
          uiOutput(paste0("FILTER_",i))
        })
      )

    })

  })


  observeEvent(input$lastSelect, {

    if (!is.null(input$lastSelectId)) {
      cat("lastSelectId:", input$lastSelectId, "\n")
      cat("lastSelectName:", input$lastSelectName, "\n")
    }  
    # selectInput id
    Filter = input$lastSelectId
    # column name of dataset, (label on select input)
    NAME = input$lastSelectName
    choices = unique(mtcars[,NAME])

    if (length(input[[Filter]]) == 0) {
      # in corresponding selectInput has no elements selected
      updateSelectInput(
        session = session, inputId = Filter, selected = as.character(choices)
      )
    } else {
      # has at least one element selected
      updateSelectInput(
        session = session, inputId = Filter, selected = ""
      )
    }

  })

  output$L = renderPrint({
    input$lastSelectId
  })
}


ui <- fluidPage(
  tags$script("$(document).on('click', '.dynamicSI button', function () {
                var id = document.getElementById(this.id).getAttribute('data');
                var name = document.getElementById(this.id).getAttribute('name');
                Shiny.onInputChange('lastSelectId',id);
                Shiny.onInputChange('lastSelectName',name);
                // to report changes on the same selectInput
                Shiny.onInputChange('lastSelect', Math.random());
                });"),  

  uiOutput("FILTERS"),
  hr(),
  uiOutput("FILTER_GROUP"),
  hr(),
  verbatimTextOutput("L")

)

shinyApp(ui = ui, server = server)

如何获得获取树子的步骤数

1 个答案: