DROP命令（Commands）实现：
/*
* Drop one or more objects.
*
* We don"t currently handle all object types here. Relations, for example,
* require special handling, because (for example) indexes have additional
* locking requirements.
*
* We look up all the objects first, and then delete them in a single
* performMultipleDeletions() call. This avoids unnecessary DROP RESTRICT
* errors if there are dependencies between them.
*/
void
RemoveObjects(DropStmt *stmt)
/*
* Dispatch function for DropStmt
*/
static void
ExecDropStmt(DropStmt *stmt, bool isTopLevel)
{
switch (stmt->removeType)
{
case OBJECT_INDEX:
if (stmt->concurrent)
PreventTransactionChain(isTopLevel,
"DROP INDEX CONCURRENTLY");
/* fall through */
case OBJECT_TABLE:
case OBJECT_SEQUENCE:
case OBJECT_VIEW:
case OBJECT_MATVIEW:
case OBJECT_FOREIGN_TABLE:
RemoveRelations(stmt);
break;
default:
RemoveObjects(stmt);
break;
}
}
/*
* standard_ProcessUtility itself deals only with utility commands for
* which we do not provide event trigger support. Commands that do have
* such support are passed down to ProcessUtilitySlow, which contains the
* necessary infrastructure for such triggers.
*
* This division is not just for performance: it"s critical that the
* event trigger code not be invoked when doing START TRANSACTION for
* example, because we might need to refresh the event trigger cache,
* which requires being in a valid transaction.
*/
void
standard_ProcessUtility(Node *parsetree,
const char *queryString,
ProcessUtilityContext context,
ParamListInfo params,
DestReceiver *dest,
char *completionTag)
/*
* ProcessUtility
* general utility function invoker
*
* parsetree: the parse tree for the utility statement
* queryString: original source text of command
* context: identifies source of statement (toplevel client command,
* non-toplevel client command, subcommand of a larger utility command)
* params: parameters to use during execution
* dest: where to send results
* completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE
* in which to store a command completion status string.
*
* Notes: as of PG 8.4, caller MUST supply a queryString; it is not
* allowed anymore to pass NULL. (If you really don"t have source text,
* you can pass a constant string, perhaps "(query not available)".)
*
* completionTag is only set nonempty if we want to return a nondefault status.
*
* completionTag may be NULL if caller doesn"t want a status string.
*/
void
ProcessUtility(Node *parsetree,
const char *queryString,
ProcessUtilityContext context,
ParamListInfo params,
DestReceiver *dest,
char *completionTag)/*
* Drop one or more obje
