C# MySql 获取行数
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MySql get number of rows
提问by MTA
I try to get number of rows from a table with this :
我尝试从表中获取行数：
string commandLine = "SELECT COUNT(*) FROM client";
using (MySqlConnection connect = new MySqlConnection(connectionStringMySql))
using (MySqlCommand cmd = new MySqlCommand(commandLine, connect))
{
connect.Open();
int count = (int)cmd.ExecuteScalar();
return count;
}
And i get the exception:
我得到了例外：
Specified cast is not valid.
Any idea how i can fix it?
知道我该如何解决吗？
采纳答案by MDMalik
Try this
尝试这个
using (MySqlCommand cmd = new MySqlCommand(commandLine, connect))
{
connect.Open();
return Convert.ToInt32(cmd.ExecuteScalar());
}
回答by Fabian Bigler
using (MySqlCommand cmd = new MySqlCommand(commandLine, connect))
{
connect.Open();
return Convert.ToInt32(cmd.ExecuteScalar());
}
EDIT:Make also sure to handle exceptions in your code (E.g. if there is SQL Connection Error).
Also, if it's not a COUNT(*)the value returned by ExecuteScalar()can be null (!)
编辑：还要确保处理代码中的异常（例如，如果存在 SQL 连接错误）。此外，如果它不是，则COUNT(*)返回的值ExecuteScalar()可以为 null (!)
回答by Michael Knowles
If you wish to use the cast, you can use:
如果你想使用演员表，你可以使用：
long count = (long)cmd.ExecuteScalar();
As mentioned above, COUNT in MySql returns BIGINT, hence casting with an int fails.
如上所述，MySql 中的 COUNT 返回 BIGINT，因此使用 int 进行转换失败。
