从SQL查询中捕获计数

Question

C#(.cs文件)中从SQL命令获取计数的最简单方法是什么

SELECT COUNT(*) FROM table_name

成int变量？

Answer 1

使用SqlCommand.ExecuteScalar()并将其投射到int:

cmd.CommandText = "SELECT COUNT(*) FROM table_name";
Int32 count = (Int32) cmd.ExecuteScalar();

Answer 2

SqlConnection conn = new SqlConnection("ConnectionString");
conn.Open();
SqlCommand comm = new SqlCommand("SELECT COUNT(*) FROM table_name", conn);
Int32 count = (Int32) comm .ExecuteScalar();

Answer 3

您将获得转换错误:

cmd.CommandText = "SELECT COUNT(*) FROM table_name";
Int32 count = (Int32) cmd.ExecuteScalar();

改为使用:

string stm = "SELECT COUNT(*) FROM table_name WHERE id="+id+";";
MySqlCommand cmd = new MySqlCommand(stm, conn);
Int32 count = Convert.ToInt32(cmd.ExecuteScalar());
if(count > 0){
    found = true; 
} else {
    found = false; 
}