Function ATPrepDropColumn

src/backend/commands/tablecmds.c:10246–10261

* ALTER TABLE DROP COLUMN * * DROP COLUMN cannot use the normal ALTER TABLE recursion mechanism, * because we have to decide at runtime whether to recurse or not depending * on whether attinhcount goes to zero or not. (We can't check this in a * static pre-pass because it won't handle multiple inheritance situations * correctly.) */

 * correctly.)
 */
static void
ATPrepDropColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
				 AlterTableCmd *cmd, LOCKMODE lockmode,
				 AlterTableUtilityContext *context)
{
	if (rel->rd_rel->reloftype && !recursing)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("cannot drop column from typed table")));

	if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
		ATTypedTableRecursion(wqueue, rel, cmd, lockmode, context);

	if (recurse)
		cmd->subtype = AT_DropColumnRecurse;
}

void
set_random_distribution_if_drop_distkey(Relation rel, AttrNumber attnum)