Function resolve_unique_index_expr

src/backend/parser/parse_clause.c:3383–3469

* resolve_unique_index_expr * Infer a unique index from a list of indexElems, for ON * CONFLICT clause * * Perform parse analysis of expressions and columns appearing within ON * CONFLICT clause. During planning, the returned list of expressions is used * to infer which unique index to use. */

 * to infer which unique index to use.
 */
static List *
resolve_unique_index_expr(ParseState *pstate, InferClause *infer,
						  Relation heapRel)
{
	List	   *result = NIL;
	ListCell   *l;

	foreach(l, infer->indexElems)
	{
		IndexElem  *ielem = (IndexElem *) lfirst(l);
		InferenceElem *pInfer = makeNode(InferenceElem);
		Node	   *parse;

		/*
		 * Raw grammar re-uses CREATE INDEX infrastructure for unique index
		 * inference clause, and so will accept opclasses by name and so on.
		 *
		 * Make no attempt to match ASC or DESC ordering or NULLS FIRST/NULLS
		 * LAST ordering, since those are not significant for inference
		 * purposes (any unique index matching the inference specification in
		 * other regards is accepted indifferently).  Actively reject this as
		 * wrong-headed.
		 */
		if (ielem->ordering != SORTBY_DEFAULT)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
					 errmsg("ASC/DESC is not allowed in ON CONFLICT clause"),
					 parser_errposition(pstate,
										exprLocation((Node *) infer))));
		if (ielem->nulls_ordering != SORTBY_NULLS_DEFAULT)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
					 errmsg("NULLS FIRST/LAST is not allowed in ON CONFLICT clause"),
					 parser_errposition(pstate,
										exprLocation((Node *) infer))));

		if (!ielem->expr)
		{
			/* Simple index attribute */
			ColumnRef  *n;

			/*
			 * Grammar won't have built raw expression for us in event of
			 * plain column reference.  Create one directly, and perform
			 * expression transformation.  Planner expects this, and performs
			 * its own normalization for the purposes of matching against
			 * pg_index.
			 */
			n = makeNode(ColumnRef);
			n->fields = list_make1(makeString(ielem->name));
			/* Location is approximately that of inference specification */
			n->location = infer->location;
			parse = (Node *) n;
		}
		else
		{
			/* Do parse transformation of the raw expression */
			parse = (Node *) ielem->expr;