I want to know if it is possible to run a SQL query which returns the number of rows round in a table. I have a page which upon clicked, it will run sql queries which compares data between 2 tables, thus I will want the user to be notified if one or more table is empty.
SqlConnection thisConnection = new SqlConnection("Data Source=DATASOURCE");
SqlCommand nonqueryCommand = thisConnection.CreateCommand();
try
{
thisConnection.Open();
//sql statement to check if a table is empty
//stores the count value in a integer X
if( X < 1 )
{
Response.Write("<script>alert('Database X is empty');</script>");
return;
}
}
Qs: Do I use Select Count(*) from Table
to retrieve the number of rows in a table?
How do I store the Count (*) value into an Integer?
Thank you in advance.
I am using SQL Server.
Try something like this:
public int CountRowsInTable()
{
string stmt = "SELECT COUNT(*) FROM dbo.YourTable";
int count = 0;
using(SqlConnection thisConnection = new SqlConnection("Data Source=DATASOURCE"))
using(SqlCommand cmdCount = new SqlCommand(stmt, thisConnection))
{
thisConnection.Open();
count = (int)cmdCount.ExecuteScalar();
thisConnection.Close();
}
return count;
}
Again: this works and gives you an accurate count - but it can be very very slow on large tables.
Alternatives:
SELECT TOP 1....
and making sure you get something back) Update: to simply check whether a table contains any rows at all, you could use this TOP 1
approach which should be really fast - even for large tables:
public bool TableContainsAnyRows()
{
// define a TOP 1 query - typically by the Primary Key of the table in question
// using AdventureWorks sample database here
string stmt = "SELECT TOP 1 [BusinessEntityID] FROM Person.Person ORDER BY [BusinessEntityID]";
bool containsAnyRows = false;
// open a connection and execute this query against the database
using(SqlConnection _con = new SqlConnection("server=.;database=AdventureWorks2008R2;integrated Security=SSPI;"))
using(SqlCommand _cmd = new SqlCommand(stmt, _con))
{
_con.Open();
// getting the result of the query
// if the table contains *any* rows, the result will *NOT* be NULL
object result = _cmd.ExecuteScalar();
_con.Close();
containsAnyRows = (result != null);
}
return containsAnyRows;
}
SELECT COUNT(*) FROM yourtable;
然后从结果中检索第一行。
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