Command States

Commands can be in one of four states:

Initial—No command text is set. A command is in this state after IDBCreateCommand::CreateCommand is called.
Unprepared—The command text is set but the command is not prepared. A command is in this state after ICommandText::SetCommandText is called.
Prepared—The command text is set and the command is prepared. A command is in this state after ICommandPrepare::Prepare is called.
Executed—The command text is executed. A command is in this state after ICommand::Execute is called.

The following table lists each state and shows the code returned by each method in a command interface when it is called in that state. This table uses the following abbreviations:

OK= S_OK
NC= DB_E_NOCOMMAND
NP= DB_E_NOTPREPARED
OO= DB_E_OPENOBJECT

Method	Initial	Unprepared	Prepared	Executed
IColumnsInfo
GetColumnInfo	NC	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)	OK	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)
MapColumnIDs	NC	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)	OK	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)
IColumnsRowset
GetAvailableColumns	NC	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)	OK	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)
GetColumnsRowset	NC	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)	OK	OK (ICommandPrepare is not supported) - or - NP (ICommandPrepare is supported)
ICommand
Cancel	OK	OK	OK	OK
Execute	NC	OK	OK	OK
GetDBSession	OK	OK	OK	OK
ICommandPrepare
Prepare	NC	OK	OK	OK (Execute did not create a rowset) - or - OO (Execute created a rowset, and the rowset is still open)
Unprepare	OK	OK	OK	OK (Execute did not create a rowset) - or - OO (Execute created a rowset, and the rowset is still open)
ICommandProperties
GetProperties	OK	OK	OK	OK
SetProperties	OK	OK	OK	OK (Execute did not create a rowset) - or - OO (Execute created a rowset, and the rowset is still open)
ICommandText
GetCommandText	NC	OK	OK	OK
SetCommandText	OK	OK	OK	OK (Execute did not create a rowset) - or - OO (Execute created a rowset, and the rowset is still open)
ICommandWithParameters
GetParameterInfo	OK (SetParameterInfo has been called) - or - NC (SetParameterInfo has not been called)	OK (SetParameterInfo has been called) - or - NP (ICommandPrepare is supported and SetParameterInfo has not been called)	OK	OK
MapParameterNames	OK (SetParameterInfo has been called) - or - NC (SetParameterInfo has not been called)	OK (SetParameterInfo has been called) - or - NP (ICommandPrepare is supported and SetParameterInfo has not been called)	OK	OK
SetParameterInfo	OK	OK	OK	OK (Execute did not create a rowset) - or - OO (Execute created a rowset, and the rowset is still open)

The following figures illustrate the state transitions for a command. The first shows the command text set to an empty string, the second to a nonempty string.

Command text set to an empty string, then a nonempty string