Function TryOptimizeDollarOrExpr

pg_documentdb/src/query/query_operator.c:4852–5002

* Optimize for common expression scenarios for $or * Currently handled optimizations: * { PATH: { $exists: false } } OR { PATH: { $eq: null } } -> { $eq: null } */

 * { PATH: { $exists: false } } OR { PATH: { $eq: null } } -> { $eq: null }
 */
static Expr *
TryOptimizeDollarOrExpr(BsonQueryOperatorContext *context,
						List *orQuals)
{
	if (list_length(orQuals) == 1)
	{
		/* $or of a single qual is the qual */
		return (Expr *) linitial(orQuals);
	}

	/* For now, only optimize when $or has 2 entries */
	if (list_length(orQuals) != 2)
	{
		return NULL;
	}

	const MongoQueryOperator *eqop = GetMongoQueryOperatorByQueryOperatorType(
		QUERY_OPERATOR_EQ, context->inputType);
	const MongoQueryOperator *existsop = GetMongoQueryOperatorByQueryOperatorType(
		QUERY_OPERATOR_EXISTS, context->inputType);

	Expr *firstArg = NULL;
	Expr *equalsNullExpr = NULL;
	StringView singlePathEqualsNull = { 0 };
	StringView singlePathExistsFalse = { 0 };
	ListCell *cell;
	foreach(cell, orQuals)
	{
		Expr *currentExpr = lfirst(cell);

		Oid funcId;
		List *args;
		if (IsA(currentExpr, FuncExpr))
		{
			FuncExpr *expr = (FuncExpr *) currentExpr;
			funcId = expr->funcid;
			args = expr->args;
		}
		else if (IsA(currentExpr, OpExpr))
		{
			OpExpr *opExpr = (OpExpr *) currentExpr;
			funcId = opExpr->opfuncid;
			args = opExpr->args;
		}
		else
		{
			return NULL;
		}

		if (funcId != eqop->postgresRuntimeFunctionOidLookup() &&
			funcId != existsop->postgresRuntimeFunctionOidLookup())
		{
			continue;
		}

		Expr *currentFirstArg = linitial(args);
		Expr *secondArg = lsecond(args);