Function _ExecutionPlan_UnionPlans

src/execution_plan/execution_plan.c:48–133

}

static ExecutionPlan *_ExecutionPlan_UnionPlans(AST *ast) {
	uint end_offset = 0;
	uint start_offset = 0;
	uint clause_count = cypher_ast_query_nclauses(ast->root);
	uint *union_indices = AST_GetClauseIndices(ast, CYPHER_AST_UNION);
	array_append(union_indices, clause_count);
	int union_count = array_len(union_indices);
	ASSERT(union_count > 1);

	// Placeholder for each execution plan, these all will be joined
	// via a single UNION operation
	ExecutionPlan *plans[union_count];

	for(int i = 0; i < union_count; i++) {
		// Create an AST segment from which we will build an execution plan.
		end_offset = union_indices[i];
		AST *ast_segment = AST_NewSegment(ast, start_offset, end_offset);
		plans[i] = ExecutionPlan_FromTLS_AST();
		AST_Free(ast_segment); // Free the AST segment.

		// Next segment starts where this one ends.
		start_offset = union_indices[i] + 1;
	}

	QueryCtx_SetAST(ast); // AST segments have been freed, set master AST in QueryCtx.

	array_free(union_indices);

	/* Join streams:
	 * MATCH (a) RETURN a UNION MATCH (a) RETURN a ....
	 * left stream:     [Scan]->[Project]->[Results]
	 * right stream:    [Scan]->[Project]->[Results]
	 *
	 * Joined:
	 * left stream:     [Scan]->[Project]
	 * right stream:    [Scan]->[Project]
	 *                  [Union]->[Distinct]->[Result] */
	ExecutionPlan *plan = ExecutionPlan_NewEmptyExecutionPlan();
	plan->record_map = raxNew();

	OpBase *results_op = NewResultsOp(plan);
	OpBase *parent = results_op;
	ExecutionPlan_UpdateRoot(plan, results_op);

	// Introduce distinct only if `ALL` isn't specified.
	const cypher_astnode_t *union_clause = AST_GetClause(ast, CYPHER_AST_UNION,
														 NULL);
	if(!cypher_ast_union_has_all(union_clause)) {
		uint clause_count = cypher_ast_query_nclauses(ast->root);
		const cypher_astnode_t *last_clause = cypher_ast_query_get_clause(ast->root, clause_count - 1);
		if(cypher_astnode_type(last_clause) == CYPHER_AST_RETURN) {
			uint projection_count = cypher_ast_return_nprojections(last_clause);
			// Build a stack array to hold the aliases to perform Distinct on
			const char *projections[projection_count];
			for(uint i = 0; i < projection_count; i++) {
				// Retrieve aliases from the RETURN clause
				const cypher_astnode_t *projection = cypher_ast_return_get_projection(last_clause, i);
				const cypher_astnode_t *alias = cypher_ast_projection_get_alias(projection);