使用本地数据库的 C# SQL 随机样本

Question

我想知道如何使用 c# 从本地数据库中随机获取 n 个样本

到目前为止我做了什么。

"SELECT TOP "+n+" QUESTION,C1,C2,C3,C4,ANSWER FROM qPIPE WHERE CONTENT = 'Topic' ORDER BY RAND()"

"SELECT QUESTION,C1,C2,C3,C4,ANSWER FROM qPIPE WHERE CONTENT = 'Topic' ORDER BY RAND() LIMIT "+n+""

错误：附加信息：表达式中未定义函数“RAND”。

"SELECT TOP "+n+" QUESTION,C1,C2,C3,C4,ANSWER FROM qPIPE WHERE CONTENT = 'Topic' ORDER BY NEWID()"

附加信息：表达式中未定义函数“NEWID”。

我的连接字符串

ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0DataSource=|DataDirectory|\questionbank.accdb";

但是当我尝试向 MS SQL 查询时

SELECT TOP n QUESTION, C1, C2, C3, C4, ANSWER FROM qPIPE WHERE CONTENT = 'Topic' ORDER BY NEWID()

它工作正常。从具有匹配主题的表中获取 n 个问题。

我正在使用 MVS 2015、MSSMS 2017。正在制作一个获胜表格。

编辑：

using ORDER BY RND()

编辑：

connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            command.CommandText = "SELECT TOP 2 QUESTION,C1,C2,C3,C4,ANSWER FROM qPIPE WHERE CONTENT = 'Thermodynamics' ORDER BY RND()";
            OleDbDataAdapter dAdap = new OleDbDataAdapter(command);
            DataTable dTable = new DataTable();
            dAdap.Fill(dTable);
            dataGridView1.DataSource = dTable;
connection.Close();

Answer 1

在 SQL Server 中，您可以使用NEWID() 函数：

SELECT TOP "+n+" QUESTION,C1,C2,C3,C4,ANSWER
FROM qPIPE
WHERE CONTENT = 'Topic'
ORDER BY NEWID();

在 MS Access 中，您可以使用RND()：

SELECT TOP "+n+" QUESTION,C1,C2,C3,C4,ANSWER
FROM qPIPE
WHERE CONTENT = 'Topic'
ORDER BY RND();

Answer 2

您应该避免连接 SQL 字符串（可能的 SQL 注入）。您可以将n 作为参数传递：

DECLARE @n INT = 5;

SELECT TOP (n) QUESTION, C1, C2, C3, C4, ANSWER
FROM qPIPE
WHERE CONTENT = 'Topic'
ORDER BY NEWID();

编辑：

根据您的连接字符串，我假设您正在连接到 MS Access 数据库。然后你可以使用ORDER BY RND(-(100000*ID)*Time())。基于kobik's comment