C# 如何计算访问数据库表的总行数？
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How to count total number of rows of an access database table?
提问by Yogita Negi
string constr = @"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=C:\Users\yogi\Documents\mydb.mdb";
string cmdstr = "select * from quant_level1";
OleDbConnection con = new OleDbConnection(constr);
OleDbCommand com = new OleDbCommand(cmdstr, con);
con.Open();
OleDbDataReader reader = com.ExecuteReader();
reader.Read();
DataSet data = new DataSet();
int i = data.Tables["quant_level1"].Rows.Count;
Label2.Text = i.ToString();
回答by Damith
use
用
string cmdstr = "SELECT COUNT(*) FROM quant_level1";
With com.ExecuteScalar()
和 com.ExecuteScalar()
using(OleDbConnection conn = new OleDbConnection(constr))
using(OleDbCommand command = new OleDbCommand(cmdstr, conn))
{
conn.Open();
int count = (int)command.ExecuteScalar();
}
ExecuteScalarreturns the first column of the first row in the result set returned by the query, here it give you row count.
ExecuteScalar返回查询返回的结果集中第一行的第一列，在这里它为您提供行数。
you can use OleDbDataReaderas you try in your code sample. but need to change the logic bit.
您可以OleDbDataReader在代码示例中尝试使用。但需要更改逻辑位。
using (OleDbConnection con = new OleDbConnection(constr))
using (OleDbCommand com = new OleDbCommand("select * from quant_level1", con))
{
con.Open();
using (OleDbDataReader myReader = com.ExecuteReader())
{
DataTable dt = new DataTable();
dt.Load(myReader);
int count = dt.Rows.Count;
}
}
Why you fail!
你为什么失败！
You have created data set but you haven't load data to dataset using your DataReader. So you will get zero row count at the end.
您已创建数据集，但尚未使用 DataReader 将数据加载到数据集。所以最后你会得到零行数。
回答by BRAHIM Kamel
You should do something like this:
你应该做这样的事情：
Select count(*) from quant_level1
Change the command syntax executescalar to retrieve a single value
更改命令语法 executescalar 以检索单个值
CommandText = "SELECT COUNT(*) FROM region";
Int32 count = (int32) ExecuteScalar();
Hope this can enlighten you a bit
希望这可以对你有所启发
回答by King King
Looks like that you want to fill your DataSetand count the rows later:
看起来您想DataSet稍后填充并计算行数：
DataSet data = new DataSet();
OleDbDataAdapter da = new OleDbDataAdapter(com);
da.Fill(data);
int i = data.Tables[0].Rows.Count;
Label2.Text = i.ToString();
If you just want to count the rows, you can change the query to SELECT COUNT(*) FROM quant_level1and get the return value like this:
如果您只想计算行数，您可以将查询更改为SELECT COUNT(*) FROM quant_level1并获取返回值，如下所示：
int i = (int) com.ExecuteScalar();
Label2.Text = i.ToString();
