vb.net中select sybase數(shù)據(jù)庫(kù)結(jié)果出來(lái)零條或者數(shù)量極少

sqlserver支持top關(guān)鍵字，返回前100條數(shù)據(jù)。select top 100 * from table;// 返回前100行數(shù)據(jù)

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mysql支持limit，一個(gè)參數(shù)：select * from table limit 100; //返回前100行記錄

Oracle需要使用rownum。select * from table where rownum=100; //返回前100條數(shù)據(jù)

TOP 子句

TOP 子句用于規(guī)定要返回的記錄的數(shù)目。

對(duì)于擁有數(shù)千條記錄的大型表來(lái)說(shuō)，TOP 子句是非常有用。

SQL Server 的語(yǔ)法：

SELECT TOP number|percent column_name(s)

FROM table_name

limit子句用于強(qiáng)制select語(yǔ)句返回置頂?shù)挠涗洈?shù)，參數(shù)必須是整數(shù)常量。一個(gè)參數(shù)是返回前幾條記錄；兩個(gè)參數(shù)時(shí)，第一個(gè)參數(shù)指定第一個(gè)返回記錄行的偏移量（初始記錄行的偏移量是0），第二個(gè)參數(shù)指定返回記錄的最大數(shù)目。

VB.NET中隨機(jī)產(chǎn)生十個(gè)數(shù)字

添加listbox1,label1,command1

Public Class Form1

Dim N(10) As Integer

'生成隨機(jī)數(shù)

Private Sub CreatRand()

Dim I As Integer

Dim Strarr As String

Strarr = ""

ListBox1.Items.Clear()

Dim R As New System.Random

For I = 0 To 9

N(I) = R.Next(30, 100)

ListBox1.Items.Add(Str(N(I)))

Strarr = Strarr Str(N(I)) " "

Next

'添加標(biāo)簽的橫向數(shù)字序列

Label1.Text = Strarr

End Sub

'獲取最大值

Private Function GetMax() As Integer

Dim I As Integer

Dim intMax As Integer

intMax = 0

For I = 0 To 9

intMax = IIf(intMax N(I), intMax, N(I))

Next

Return intMax

End Function

'獲取最小值

Private Function GetMin() As Integer

Dim I As Integer

Dim intMin As Integer

intMin = 101

For I = 0 To 9

intMin = IIf(intMin N(I), intMin, N(I))

Next

Return intMin

End Function

'獲取平均值

Private Function GetAve() As Single

Dim I As Integer

Dim Sum As Integer

Sum = 0

For I = 0 To 9

Sum = Sum + N(I)

Next

Return Sum / 10

End Function

'生成隨機(jī)數(shù)，顯示各種值

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Call CreatRand()

MsgBox("最大值=" Str(GetMax()) ",最小值=" Str(GetMin()) ",平均值=" Str(GetAve()))

End Sub

End Class

VB.net隨機(jī)產(chǎn)生10個(gè)小于數(shù)字不重復(fù)

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim i, j

j = GetRndNotRepeat(1, 10, 10)

If j(0) Then

For i = 1 To 10

MsgBox(j(i))

Next

End If

End Sub

Public Function GetRndNotRepeat(ByVal NumMin As Integer, ByVal NumMax As Integer, ByVal n As Integer)

'編制:xsfhlzh

'功能:取NumMin到NumMax間的n個(gè)隨機(jī)整數(shù)

'說(shuō)明:取數(shù)標(biāo)志數(shù)組是Byte，每一位表示NumMin到NumMax間某個(gè)數(shù)的狀態(tài)

Dim arr() As Integer

If n NumMax - NumMin + 1 Then

ReDim arr(0)

arr(0) = 0

Return arr

Else

ReDim arr(n)

Dim m As Integer

Dim b() As Byte

m = Int((NumMax - NumMin) / 8)

ReDim b(m)

'取數(shù)標(biāo)志

Dim i

Dim x, y, z As Integer

Randomize()

arr(0) = 1

For i = 1 To n

Do

'找到x的位置，y表示x在數(shù)組的第幾個(gè)字節(jié)，z表示x在該字節(jié)的第幾位

x = Int(Rnd() * (NumMax - NumMin + 1)) + NumMin

y = x - NumMin

z = 2 ^ (y Mod 8)

y = y \ 8

Loop While b(y) And z

b(y) = b(y) Or z

arr(i) = x

'找到未取的數(shù)，并放入數(shù)組，設(shè)置標(biāo)志位

Next i

End If

Return arr

End Function