Function transformStatsStmt

src/backend/parser/parse_utilcmd.c:4039–4102

* transformStatsStmt - parse analysis for CREATE STATISTICS * * To avoid race conditions, it's important that this function relies only on * the passed-in relid (and not on stmt->relation) to determine the target * relation. */

 * relation.
 */
CreateStatsStmt *
transformStatsStmt(Oid relid, CreateStatsStmt *stmt, const char *queryString)
{
	ParseState *pstate;
	ParseNamespaceItem *nsitem;
	ListCell   *l;
	Relation	rel;

	/* Nothing to do if statement already transformed. */
	if (stmt->transformed)
		return stmt;

	/* Set up pstate */
	pstate = make_parsestate(NULL);
	pstate->p_sourcetext = queryString;

	/*
	 * Put the parent table into the rtable so that the expressions can refer
	 * to its fields without qualification.  Caller is responsible for locking
	 * relation, but we still need to open it.
	 */
	rel = relation_open(relid, NoLock);
	nsitem = addRangeTableEntryForRelation(pstate, rel,
										   AccessShareLock,
										   NULL, false, true);

	/* no to join list, yes to namespaces */
	addNSItemToQuery(pstate, nsitem, false, true, true);

	/* take care of any expressions */
	foreach(l, stmt->exprs)
	{
		StatsElem  *selem = (StatsElem *) lfirst(l);

		if (selem->expr)
		{
			/* Now do parse transformation of the expression */
			selem->expr = transformExpr(pstate, selem->expr,
										EXPR_KIND_STATS_EXPRESSION);

			/* We have to fix its collations too */
			assign_expr_collations(pstate, selem->expr);
		}
	}

	/*
	 * Check that only the base rel is mentioned.  (This should be dead code
	 * now that add_missing_from is history.)
	 */
	if (list_length(pstate->p_rtable) != 1)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
				 errmsg("statistics expressions can refer only to the table being referenced")));

	free_parsestate(pstate);

	/* Close relation */
	table_close(rel, NoLock);