将SELECT COUNT(*)语句结果放入int变量

Question

我有一个SELECT COUNT(*)声明,C#/ASP.NET我想将结果存储为int用作IF条件.但是我在visual studio中遇到错误:

错误:System.Data.SqlClient.SqlException(0x80131904):数据类型text和varchar在等于运算符中不兼容.在System.Data.SqlClient.SqlConnection.

它告诉我它发生在int temp行.我在数据库表中访问的列是文本类型.

conn.Open();    
String checkEmail = "select count(*) from Players where PlayerEmail= '" + txtEmailLogIn.Text + "'";
SqlCommand com = new SqlCommand(checkEmail, conn);
int temp = Convert.ToInt32(com.ExecuteScalar().ToString());
conn.Close();
if (temp > 0) 
{

}

Answer 1

问题出在您的SQL中.=比较TEXT数据类型时不能使用,而是可以使用LIKE:

String checkEmail = "select count(*) from Players where PlayerEmail LIKE '" + txtEmailLogIn.Text + "'";

但是要注意,在编写像这样的SQL字符串时,你正在打开SQL注入攻击.