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How to pass a timestamp value to or from SQL Server with ODBC API


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This article was previously published under Q249819

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Summary

The SQL Server data type timestamp is a column value that is automatically updated every time a row is inserted or updated. Values in timestamp columns are not date/time data. By default, they are defined as binary(8) (for non nullable columns) or varbinary(8) (for nullable columns), which indicates the sequence of Microsoft SQL Server activity on the row. A table can have only one timestamp column.

From an ODBC application you can retrieve the value stored in a timestamp column and you can also send a timestamp parameter. You can not bind the timestamp column to SQL_TYPE_TIMESTAMP from an ODBC application. SQL_TYPE_TIMESTAMP is a totally different data type that is actually used for date/time data, and it does not correspond to the timestamp data type in SQL Server.

To pass a parameter of type timestamp to SQL Server, you have to bind a parameter of type SQL_BINARY with a column size of 8. You can also bind the timestamp value with a SQL_CHAR parameter.

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More information

The following ODBC example illustrates the functionality described in the "Summary" section. In this example you bind the timestamp parameter as SQL_BINARY. The example retrieves some data from a table that contains a timestamp column, and then queries the same table and passes a timestamp parameter.

The example assumes the following:
  • You have a data source name (DSN) named LocalServer.

  • You have run the following SQL script to create a table and insert a value:

    if exists (select * from sysobjects where id = object_id('dbo.TTimeStamp') and sysstat & 0xf = 3)
    	drop table dbo.TTimeStamp
    GO
    
    CREATE TABLE dbo.TTimeStamp (
    	col1 char (10) NOT NULL ,
    	myTimeStamp timestamp NOT NULL 
    )
    GO
    
    Insert into TTimestamp (col1) values("hello")
    GO
    					

Sample Code

#include <windows.h>
#include <stdio.h>
#include <sql.h>
#include <sqlext.h>

int main(int argc, char* argv[])
{
	SQLCHAR*               theDiagState = new SQLCHAR[50];
	SQLINTEGER             theNativeState;
	SQLCHAR*               theMessageText  = new SQLCHAR[255];
	SQLSMALLINT            iOutputNo;

	SQLHENV                m_SQLEnvironment;
	SQLHDBC                m_SQLConnection;
	SQLHSTMT               m_SQLStatement;

	SQLRETURN              iReturn;
	SQLINTEGER             iData;
	SQLCHAR*               cData = new SQLCHAR[20];
	SQLCHAR*               cData1 = new SQLCHAR[20];
	SQLCHAR*               cMyTimeStamp = new SQLCHAR[20];





	//Connect
	//Allocate Environment Handle
	iReturn = SQLAllocHandle(SQL_HANDLE_ENV,SQL_NULL_HANDLE,&m_SQLEnvironment);

	//Set environment to ODBC_3
	iReturn = SQLSetEnvAttr(m_SQLEnvironment,SQL_ATTR_ODBC_VERSION,(SQLPOINTER) SQL_OV_ODBC3,0);

	//Allocate connection handle
	iReturn = SQLAllocHandle(SQL_HANDLE_DBC,m_SQLEnvironment,&m_SQLConnection);

	//Connect to the database.
	//In this example we have used the following:
	//LocalServer as the DSN name.
	//LoginName is a placeholder for the login name. Password is a placeholder for the password to the LoginName.
	//CHANGE THE DSN NAME and UserId and Password here.
	
	iReturn = SQLConnect(m_SQLConnection,(SQLCHAR*) "LocalServer",SQL_NTS,(SQLCHAR*)"LoginName",SQL_NTS,(SQLCHAR*)"Password",SQL_NTS);
	if (iReturn != SQL_ERROR)
	{
	
		//Run the query.
		//Allocate the statement handle.
		iReturn = SQLAllocHandle(SQL_HANDLE_STMT,m_SQLConnection,&m_SQLStatement);

                
		//CHANGE THE TABLE/COLUMN NAME HERE.
		//In this case we have used a table named TTimeStamp in SQL Server 6.5 or SQL Server 7.0 with two fields.
		//Col1 = Char(10) Primary
		//myTimeStamp = TimeStamp


		//Execute the statement to get some timestamp value.

		iReturn = SQLExecDirect(m_SQLStatement,(SQLCHAR*) "Select * from TTimeStamp",SQL_NTS);
		iReturn = SQLBindCol(m_SQLStatement,2,SQL_C_CHAR,cData,17,&iData);
		while( TRUE)
		{
			iReturn = SQLFetch(m_SQLStatement);
			if (!((iReturn == SQL_SUCCESS) || (iReturn == SQL_SUCCESS_WITH_INFO)))
				break;

		}
		//Copying timestamp data to another location. This saves the last time stamp value. We will use this 
		//to query the table a second time.
		strcpy((char*)cMyTimeStamp, (const char*) cData);
		iReturn = SQLCancel(m_SQLStatement);

		iData = SQL_NTS;
		iReturn = SQLBindParameter(m_SQLStatement,1,SQL_PARAM_INPUT,SQL_C_CHAR,SQL_BINARY,8,0,cMyTimeStamp,0,&iData);  	
		//Executing select statement with the timestamp as parameter.
		iReturn = SQLExecDirect(m_SQLStatement,(SQLCHAR*) "Select * from tTimeStamp where myTimeStamp = ?",SQL_NTS);
		if (iReturn != SQL_SUCCESS)
		{
			SQLGetDiagRec(SQL_HANDLE_STMT,m_SQLStatement,1,theDiagState,&theNativeState,theMessageText,100,&iOutputNo);

		}
		//Bind the column again to see the data.
		iReturn = SQLBindCol(m_SQLStatement,2,SQL_C_CHAR,cData1,17,&iData);
		while( TRUE)
		{
			//We will get only one record this time.
			iReturn = SQLFetch(m_SQLStatement);
			if (!((iReturn == SQL_SUCCESS) || (iReturn == SQL_SUCCESS_WITH_INFO)))
				break;

		}
				


		//DISCONNECT

		iReturn = SQLFreeHandle(SQL_HANDLE_STMT,m_SQLStatement);
		iReturn = SQLDisconnect(m_SQLConnection);
		iReturn = SQLFreeHandle(SQL_HANDLE_DBC,m_SQLConnection);
		iReturn = SQLFreeHandle(SQL_HANDLE_ENV,m_SQLEnvironment);

		m_SQLStatement = NULL;
		m_SQLConnection = NULL;
		m_SQLEnvironment = NULL;
	}
	else
	{
		//If it fails to connect theMessageText contains the reason for the failure.
		SQLGetDiagRec(SQL_HANDLE_DBC,m_SQLConnection,1,theDiagState,&theNativeState,theMessageText,100,&iOutputNo);

	}
	
	delete cData;
	delete cData1;
	delete cMyTimeStamp;
	delete theMessageText; 
	delete theDiagState;
	return 1;

}

				
The preceding example retrieves some data from a table named TTimeStamp. It then runs a query that retrieves a particular record from the table depending upon a timestamp value.

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References

For more information, click the following article number to view the article in the Microsoft Knowledge Base:
170380� How to display/pass TimeStamp value from/to SQL Server

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Keywords: KB249819, kbhowto, kbdatabase

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Article Info
Article ID : 249819
Revision : 7
Created on : 7/31/2006
Published on : 7/31/2006
Exists online : False
Views : 575