Function ATExecSetStatistics

src/backend/commands/tablecmds.c:9882–9995

* ALTER TABLE ALTER COLUMN SET STATISTICS * * Return value is the address of the modified column */

 * Return value is the address of the modified column
 */
static ObjectAddress
ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newValue, LOCKMODE lockmode)
{
	int			newtarget;
	Relation	attrelation;
	HeapTuple	tuple;
	Form_pg_attribute attrtuple;
	AttrNumber	attnum;
	ObjectAddress address;

	/*
	 * We allow referencing columns by numbers only for indexes, since table
	 * column numbers could contain gaps if columns are later dropped.
	 */
	if (rel->rd_rel->relkind != RELKIND_INDEX &&
		rel->rd_rel->relkind != RELKIND_PARTITIONED_INDEX &&
		!colName)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot refer to non-index column by number")));

	Assert(IsA(newValue, Integer));
	newtarget = intVal(newValue);

	/*
	 * Limit target to a sane range
	 */
	if (newtarget < -1)
	{
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("statistics target %d is too low",
						newtarget)));
	}
	else if (newtarget > 10000)
	{
		newtarget = 10000;
		ereport(WARNING,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("lowering statistics target to %d",
						newtarget)));
	}

	attrelation = table_open(AttributeRelationId, RowExclusiveLock);

	if (colName)
	{
		tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);

		if (!HeapTupleIsValid(tuple))
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_COLUMN),
					 errmsg("column \"%s\" of relation \"%s\" does not exist",
							colName, RelationGetRelationName(rel))));
	}
	else
	{
		tuple = SearchSysCacheCopyAttNum(RelationGetRelid(rel), colNum);