选择语句的返回值 [英] Return value of a select statement

问题描述

我想将 select 语句的结果值检索到字符串变量中.像这样:

I want to retrieve the resulting value of a select statement into a string variable. Like this:

OleDbCommand cmd1 = new OleDbCommand();
cmd1.Connection = GetConnection();
cmd1.CommandText = "SELECT treatment FROM appointment WHERE patientid = " + text;
cmd1.ExecuteNonQuery();
        

我想将选定的治疗值放入字符串变量中.我该怎么做?

I want to place the selected treatment value into a string variable. How can I do this?

推荐答案

使用 ExecuteReader() 而不是 ExecuteNonQuery().ExecuteNonQuery() 仅返回受影响的行数.

Use ExecuteReader() and not ExecuteNonQuery(). ExecuteNonQuery() returns only the number of rows affected.

try
{
    SqlDataReader dr = cmd1.ExecuteReader();
}
catch (SqlException oError)
{

}
while(dr.Read())
{
    string treatment = dr[0].ToString();
}

或者更好，使用 using 声明 因为它.

Or better, use a using statement for it.

using(SqlDataReader dr = cmd1.ExecuteReader())
{
    while(dr.Read())
    {
        string treatment = dr[0].ToString();
    }
}

但如果您的 SqlCommand 仅返回 1 列，您可以使用 ExecuteScalar() 方法.它返回第一行的第一列，如下所示:-

But if your SqlCommand returns only 1 column, you can use the ExecuteScalar() method. It returns first column of the first row as follows:-

cmd.CommandText = "SELECT treatment FROM appointment WHERE patientid = " + text;
string str = Convert.ToString(cmd.ExecuteScalar());

您也可以打开您的代码以SQL 注入.始终使用参数化查询.Jeff 有一篇很酷的博客文章，名为 给我参数化的 SQL，否则给我死.请仔细阅读.另请阅读 DotNetPerl SqlParameter 文章.SQL 注入在您处理查询时非常重要.

Also you can open your code to SQL Injection. Always use parameterized queries. Jeff has a cool blog article called Give me parameterized SQL, or give me death. Please read it carefully. Also read DotNetPerl SqlParameter article. SQL Injection very important when you are working queries.

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