VB.Net Datatable選擇MID功能

Question

我試圖從數據表中提取所有行，其中「代碼」遵循模式「Z ## A」。我嘗試了以下無濟於事：「表達式包含未定義 函數調用中期（）」

Dim floods() As DataRow = arqTable.Select("mid(code,1,1)='Z' and isnumeric(mid(code,2,2)) and mid(code,4,1)='A'") 

返回錯誤

我能經過行使用FOR EACH循環，但我只是好奇，如果有一種方法可以簡單地使用數據表中選擇功能。

*編輯：順便說一句，使用「代碼如'Z％A'」是不會工作，因爲我特別尋找Z [數] [數] A而不是與Z [字母] [字母]一個。

Answer 1

這一個工程

Dim r1() As DataRow = dt.Select("code LIKE 'Z%' and code LIKE '%A' and substring(code, 2, 1) >= '0' and substring(code, 2, 1) <= '9' and substring(code, 3, 1) >= '0' AND substring(code, 3, 1) <= '9' and len(code) = 4 ") 

如果你在所有關心效率看看這個簡單的例子從一個興趣點性能角度。 （粘貼到控制檯應用程序中）。

結果...

1000 RECORDS... 
SELECT: 00:00:00.0050357 matches 141 
VBLIKE: 00:00:00.0021198 matches 141 - %250.0 
VBRAW: 00:00:00.0007444 matches 141 - Infinity 
CREGEX: 00:00:00.0014745 matches 141 - %500.0 

10000 RECORDS... 
SELECT: 00:00:00.0530854 matches 1430 
VBLIKE: 00:00:00.0280535 matches 1430 - %189.3 
VBRAW: 00:00:00.0067957 matches 1430 - %883.3 
CREGEX: 00:00:00.0026389 matches 1430 - %2650.0 

100000 RECORDS... 
SELECT: 00:00:00.6141986 matches 13929 
VBLIKE: 00:00:00.1773157 matches 13929 - %346.9 
VBRAW: 00:00:00.0699633 matches 13929 - %889.9 
CREGEX: 00:00:00.0271444 matches 13929 - %2274.1 

1000000 RECORDS... 
SELECT: 00:00:06.2316807 matches 138987 
VBLIKE: 00:00:01.7882370 matches 138987 - %348.5 
VBRAW: 00:00:00.7093068 matches 138987 - %878.8 
CREGEX: 00:00:00.2714249 matches 138987 - %2299.3 

代碼

Imports System.Text.RegularExpressions 

Module Module1 

    Public RegEx_Code As New Regex("^Z[0-9][0-9]A$", RegexOptions.Compiled) 

    Sub Main() 
     Dim trials() As Integer = {1000, 10000, 100000, 1000000} 'data sizes to test 
     For Each recCnt As Integer In trials 
      'build test data that is sort of similar. 
      Dim dt As New DataTable 
      dt.Columns.Add("code", GetType(String)) 
      For iQ As Integer = 0 To recCnt - 1 
       dt.Rows.Add(If(iQ Mod 4 = 0, "Z", "X") & Chr(Int(Rnd() * 15) + 48) & Chr(Int(Rnd() * 12) + 48) & If(iQ Mod 2 = 0, "A", "Y")) 
      Next 

      'test SELECT 
      Dim sw1 As Stopwatch = Stopwatch.StartNew 
      Dim r1() As DataRow = dt.Select("code LIKE 'Z%' and code LIKE '%A' and substring(code, 2, 1) >= '0' and substring(code, 2, 1) <= '9' and substring(code, 3, 1) >= '0' AND substring(code, 3, 1) <= '9' and len(code) = 4 ") 
      sw1.Stop() 

      'test VB built in LIKE 
      Dim sw2 As Stopwatch = Stopwatch.StartNew 
      Dim r2 As New List(Of DataRow)(recCnt \ 20) 
      Dim rInd2 As Integer = dt.Columns("code").Ordinal 
      For Each r As DataRow In dt.Rows 
       If CStr(r(rInd2)) Like "Z##A" Then 
        r2.Add(r) 
       End If 
      Next 
      r2.TrimExcess() 
      sw2.Stop() 

      Dim sw3 As Stopwatch = Stopwatch.StartNew 
      Dim r3 As New List(Of DataRow)(recCnt \ 20) 
      Dim rInd3 As Integer = dt.Columns("code").Ordinal 
      For Each r As DataRow In dt.Rows 
       Dim value As String = CStr(r(rInd3)) 
       If value.Length = 4 AndAlso IsNumeric(value.Substring(1, 1)) AndAlso IsNumeric(value.Substring(2, 1)) AndAlso value.StartsWith("Z") AndAlso value.EndsWith("A") Then 
        r3.Add(r) 
       End If 
      Next 
      r3.TrimExcess() 
      sw3.Stop() 

      'test Compiled Regular Expression. 
      Dim sw4 As Stopwatch = Stopwatch.StartNew 
      Dim r4 As New List(Of DataRow)(recCnt \ 20) 
      Dim rInd4 As Integer = dt.Columns("code").Ordinal 
      For Each r As DataRow In dt.Rows 
       If RegEx_Code.IsMatch(CStr(r(rInd4))) Then 
        r4.Add(r) 
       End If 
      Next 
      r4.TrimExcess() 
      sw4.Stop() 
      Console.WriteLine(recCnt & " RECORDS...") 
      Console.WriteLine("SELECT: " & sw1.Elapsed.ToString & " matches " & r1.Length) 
      Console.WriteLine("VBLIKE: " & sw2.Elapsed.ToString & " matches " & r2.Count & " - " & CDbl(sw1.ElapsedMilliseconds/sw2.ElapsedMilliseconds).ToString("%0.0")) 
      Console.WriteLine("VBRAW: " & sw3.Elapsed.ToString & " matches " & r3.Count & " - " & CDbl(sw1.ElapsedMilliseconds/sw3.ElapsedMilliseconds).ToString("%0.0")) 
      Console.WriteLine("CREGEX: " & sw4.Elapsed.ToString & " matches " & r3.Count & " - " & CDbl(sw1.ElapsedMilliseconds/sw4.ElapsedMilliseconds).ToString("%0.0")) 
      Console.WriteLine() 

     Next 

     Console.ReadLine() 
    End Sub 

End Module 

Answer 2

這工作：

arqTable.Select("code LIKE 'Z%' and code LIKE '%A' and substring(code, 2, 1) BETWEEN '0' AND '9' and substring(code, 3, 1) BETWEEN '0' AND '9'") 

Answer 3

嗨 您可以使用解決方案通過米爾恰Dogaru

建議作爲 arqTable.Select（「代碼LIKE 'Z％' 和代碼LIKE '％A'和子串（碼，2，1）之間的 '0' AND '9' 和子串（碼，3，1）之間的 '0' 和 '9「'）

與一個條件 長度（代碼）= 4

爲follow--

arqTable.Select("code LIKE 'Z%' and code LIKE '%A' and substring(code, 2, 1) BETWEEN 
'0' AND '9' and substring(code, 3, 1) BETWEEN '0' AND '9' and length(code) = 4 ")