Question

如何从C#中检查我的表是否为空？

我有这样的东西：

public MySqlConnection con;
public MySqlCommand cmd;

 con = new MySqlConnection(GetConnectionString());
 con.Open();
 cmd = new MySqlCommand("SELECT * FROM data;", con);

或者我不需要调用SELECT语句？

Answer 1

您可以在没有WHERE关闭的情况下使用COUNT（*）

或者，您可以执行一个没有WHERE子句的SELECT（id）FROM表名

Answer 2

我举一个C#的例子，祝你好运

public bool checkEmptyTable(){
        try
        {
            MySql.Data.MySqlClient.MySqlCommand com = new MySql.Data.MySqlClient.MySqlCommand();
            conn = new MySql.Data.MySqlClient.MySqlConnection("YOUR CONNECTION");
            com.Connection = conn;
            com.CommandText = "SELECT COUNT(*) from data";

            int result = int.Parse(com.ExecuteScalar().ToString());

            return result == 0; // if result equals zero, then the table is empty
        }
        finally
        {
            conn.Close();
        }
   }

Answer 3

如果数据可能是一个大表，你最好这样做（其中pkdata是你的主键字段）

SELECT COUNT(*) FROM data WHERE pkdata = (SELECT pkdata FROM data LIMIT 1);

This will run very quickly whether you have 0 rows in data or millions of rows. Using SELECT with no WHERE or ORDER BY means it just pulls the first row available, LIMIT 1 stops it getting more than 1. Maybe something to look for if you have a program that ran very quickly six months ago but now runs like a dog in treacle!

Answer 4

SELECT COUNT(*) 
FROM table 
WHERE `col_name` IS NOT NULL

友情链接