Fix multi-shard SELECT problem with HAVING clauses

Because Vars from HAVING clauses weren't being included in the remote
query's target list, they would be NULL if they did not appear in the
target list or a GROUP/ORDER clause. This change includes them in the
remote target list so they'll be available for local evaluation of the
HAVING clause.

expected/queries.out

@@ -193,6 +193,7 @@ SELECT COUNT(*) FROM articles;
     50
 (1 row)
 
+-- try query with more SQL features
 SELECT author_id, sum(word_count) AS corpus_size FROM articles
 	GROUP BY author_id
 	HAVING sum(word_count) > 25000
@@ -220,6 +221,20 @@ LOG:  distributed statement: SELECT NULL::unknown FROM ONLY articles_10036 WHERE
 
 SET client_min_messages = DEFAULT;
 SET pg_shard.log_distributed_statements = DEFAULT;
+-- use HAVING without its variable in target list
+SELECT author_id FROM articles
+	GROUP BY author_id
+	HAVING sum(word_count) > 50000
+	ORDER BY author_id;
+ author_id 
+-----------
+         2
+         4
+         6
+         8
+        10
+(5 rows)
+
 -- verify temp tables used by cross-shard queries do not persist
 SELECT COUNT(*) FROM pg_class WHERE relname LIKE 'pg_shard_temp_table%' AND
 									relkind = 'r';

pg_shard.c

@@ -709,6 +709,7 @@ RowAndColumnFilterQuery(Query *query, List *remoteRestrictList, List *localRestr
 	List *rangeTableList = NIL;
 	List *whereColumnList = NIL;
 	List *projectColumnList = NIL;
+	List *havingClauseColumnList = NIL;
 	List *requiredColumnList = NIL;
 	ListCell *columnCell = NULL;
 	List *uniqueColumnList = NIL;
@@ -731,11 +732,16 @@ RowAndColumnFilterQuery(Query *query, List *remoteRestrictList, List *localRestr
 
 	/* as well as any used in projections (GROUP BY, etc.) */
 	projectColumnList = pull_var_clause((Node *) query->targetList, aggregateBehavior,
-	                                    placeHolderBehavior);
+										placeHolderBehavior);
+
+	/* finally, need those used in any HAVING quals */
+	havingClauseColumnList = pull_var_clause(query->havingQual, aggregateBehavior,
+	                                         placeHolderBehavior);
 
 	/* put them together to get list of required columns for query */
 	requiredColumnList = list_concat(requiredColumnList, whereColumnList);
 	requiredColumnList = list_concat(requiredColumnList, projectColumnList);
+	requiredColumnList = list_concat(requiredColumnList, havingClauseColumnList);
 
 	/* ensure there are no duplicates in the list  */
 	foreach(columnCell, requiredColumnList)

sql/queries.sql

@@ -131,6 +131,7 @@ SELECT * FROM  (articles INNER JOIN authors ON articles.id = authors.id);
 -- test cross-shard queries
 SELECT COUNT(*) FROM articles;
 
+-- try query with more SQL features
 SELECT author_id, sum(word_count) AS corpus_size FROM articles
 	GROUP BY author_id
 	HAVING sum(word_count) > 25000
@@ -146,6 +147,12 @@ SELECT count(*) FROM articles WHERE word_count > 10000;
 SET client_min_messages = DEFAULT;
 SET pg_shard.log_distributed_statements = DEFAULT;
 
+-- use HAVING without its variable in target list
+SELECT author_id FROM articles
+	GROUP BY author_id
+	HAVING sum(word_count) > 50000
+	ORDER BY author_id;
+
 -- verify temp tables used by cross-shard queries do not persist
 SELECT COUNT(*) FROM pg_class WHERE relname LIKE 'pg_shard_temp_table%' AND
 									relkind = 'r';